some exercises

Reviewed-on: https://codeberg.org/ziglings/exercises/pulls/95

.devcontainer/devcontainer.json

@@ -0,0 +1,31 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/debian
+{
+	"name": "Ziglings",
+	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+	"image": "mcr.microsoft.com/devcontainers/base:bullseye",
+	"features": {
+		"ghcr.io/devcontainers-contrib/features/zig:1": {
+			"version": "master"
+		}
+	},
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"ziglang.vscode-zig"
+			]
+		}
+	}
+
+	// Features to add to the dev container. More info: https://containers.dev/features.
+	// "features": {},
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}

.gitignore

@@ -2,3 +2,4 @@
 /zig-out/
 /answers/
 /patches/healed/
+/output/

.woodpecker/eowyn.yaml

@@ -0,0 +1,9 @@
+steps:
+  - name: eowyn
+    image: ziglings/ziglang:latest
+    pull: true
+    commands:
+      - sh ./patches/eowyn.sh
+    when:
+      event: [push, cron]
+      cron: daily*

.woodpecker/eowyn.yml

@@ -1,11 +0,0 @@
-steps:
-  eowyn:
-    image: ziglings/ziglang
-    commands:
-      - sh ./patches/eowyn.sh
-    when:
-      events:
-        - push
-        - pull-requests
-        - cron
-      cron: "Daily"

CONTRIBUTING.md

@@ -54,13 +54,12 @@ Ziglings. Please file an issue...or make a pull request!
 
 ## Formatting
 
-All exercises should conform to `zig fmt`. I often forget to do
-this.
+All exercises should conform to `zig fmt`.
 
 
 ## Pull Request Workflow
 
-Ziglings uses the "standard" Github workflow as guided by the Web
+Ziglings uses the "standard" Codeberg workflow as guided by the Web
 interface.  Specifically:
 
 * Fork this repository
@@ -71,7 +70,7 @@ interface.  Specifically:
       `git push origin my-branch`
 * Create a pull request from your branch to `ziglings/main`
 * Your faithful Ziglings maintainers will take a look at your
-  request ASAP (we don't talk about May-July 2022, LOL)
+  request ASAP (we don't talk about May-July, LOL)
 * Once the changes are reviewed, your request will be merged and
   eternal Ziglings contributor glory is yours!
 

README.md

@@ -1,12 +1,4 @@
 # Ziglings
-# ⚠️ Ziglings has moved from GitHub to Codeberg!
-
-You are looking at the current Ziglings repo if you are viewing
-this at https://codeberg.org/ziglings/exercises/
-
-You can also use the handy URL https://ziglings.org to get here!
-
-***
 
 Welcome to Ziglings! This project contains a series of tiny
 broken programs (and one nasty surprise).  By fixing them, you'll
@@ -39,6 +31,7 @@ for more detail:
 * https://ziglang.org/learn/
 * https://ziglearn.org/
 * https://ziglang.org/documentation/master/
+* [Zig in Depth! (video series)](https://www.youtube.com/watch?v=MMtvGA1YhW4&list=PLtB7CL7EG7pCw7Xy1SQC53Gl8pI7aDg9t&pp=iAQB)
 
 Also, the [Zig community](https://github.com/ziglang/zig/wiki/Community)
 is incredibly friendly and helpful!
@@ -53,7 +46,7 @@ Verify the installation and build number of `zig` like so:
 
 ```
 $ zig version
-0.12.0-dev.xxxx+xxxxxxxxx
+0.13.0-dev.xxxx+xxxxxxxxx
 ```
 
 Clone this repository with Git:
@@ -75,11 +68,14 @@ reading these.
 
 ## A Note About Versions
 
+**Hint:** To check out Ziglings for a stable release of Zig, you can use
+the appropriate tag. 
+
 The Zig language is under very active development. In order to be
 current, Ziglings tracks **development** builds of the Zig
 compiler rather than versioned **release** builds. The last
-stable release was `0.11.0`, but Ziglings needs a dev build with
-pre-release version "0.12.0" and a build number at least as high
+stable release was `0.12.0`, but Ziglings needs a dev build with
+pre-release version "0.13.0" and a build number at least as high
 as that shown in the example version check above.
 
 It is likely that you'll download a build which is _greater_ than
@@ -92,7 +88,13 @@ that if you update one, you may need to also update the other.
 
 ### Version Changes
 
-Version-0.11.0-dev.4246+71dfce31b
+Version-0.12.0-dev.3518
+* *2024-03-21* zig 0.12.0-dev.3518 - change to @fieldParentPtr - see [#19470](https://github.com/ziglang/zig/pull/19470)
+* *2024-03-21* zig 0.12.0-dev.3397 - rename std.os to std.posix - see [#5019](https://github.com/ziglang/zig/issues/5019)
+* *2024-03-14* zig 0.12.0-dev.3302 - changes in `std.fmt` - floating-point formatting implementation - see [#19229](https://github.com/ziglang/zig/pull/19229)
+* *2024-02-05* zig 0.12.0-dev.2618 - changes in `build system` - from `Step.zig_exe` to `Step.graph.zig_exe` - see [#18778](https://github.com/ziglang/zig/issues/18778)
+* *2024-01-05* zig 0.12.0-dev.2043 - rename of `std.Build.FileSource` to `std.Build.LazyPath` - see [#16353](https://github.com/ziglang/zig/issues/16353)
+* *2023-10-24* zig 0.12.0-dev.1243 - changes in `std.ChildProcess`: renamed exec to run - see [#5853](https://github.com/ziglang/zig/issues/5853)
 * *2023-06-26* zig 0.11.0-dev.4246 - changes in compile step (now it can be null)
 * *2023-06-26* zig 0.11.0-dev.3853 - removal of destination type from all cast builtins
 * *2023-06-20* zig 0.11.0-dev.3747 - `@enumToInt` is now `@intFromEnum` and `@intToFloat` is now `@floatFromInt`
@@ -209,13 +211,14 @@ Zig Core Language
 * [X] Interfaces
 * [X] Bit manipulation
 * [X] Working with C
-* [ ] Interfaces part 2
+* [X] Threading
 
 Zig Standard Library
 
 * [X] String formatting
 * [X] Testing
 * [X] Tokenization
+* [X] File handling
 
 ## Contributing
 

build.zig

@@ -15,7 +15,7 @@ const print = std.debug.print;
 //     1) Getting Started
 //     2) Version Changes
 comptime {
-    const required_zig = "0.11.0-dev.4246";
+    const required_zig = "0.12.0-dev.3518";
     const current_zig = builtin.zig_version;
     const min_zig = std.SemanticVersion.parse(required_zig) catch unreachable;
     if (current_zig.order(min_zig) == .lt) {
@@ -119,7 +119,7 @@ pub const logo =
 ;
 
 pub fn build(b: *Build) !void {
-    if (!validate_exercises()) std.os.exit(2);
+    if (!validate_exercises()) std.process.exit(2);
 
     use_color_escapes = false;
     if (std.io.getStdErr().supportsAnsiEscapeCodes()) {
@@ -172,7 +172,7 @@ pub fn build(b: *Build) !void {
         // Named build mode: verifies a single exercise.
         if (n == 0 or n > exercises.len - 1) {
             print("unknown exercise number: {}\n", .{n});
-            std.os.exit(2);
+            std.process.exit(2);
         }
         const ex = exercises[n - 1];
 
@@ -247,7 +247,7 @@ const ZiglingStep = struct {
     fn make(step: *Step, prog_node: *std.Progress.Node) !void {
         // NOTE: Using exit code 2 will prevent the Zig compiler to print the message:
         // "error: the following build command failed with exit code 1:..."
-        const self = @fieldParentPtr(ZiglingStep, "step", step);
+        const self: *ZiglingStep = @alignCast(@fieldParentPtr("step", step));
 
         if (self.exercise.skip) {
             print("Skipping {s}\n\n", .{self.exercise.main_file});
@@ -262,7 +262,7 @@ const ZiglingStep = struct {
                 print("\n{s}Ziglings hint: {s}{s}", .{ bold_text, hint, reset_text });
 
             self.help();
-            std.os.exit(2);
+            std.process.exit(2);
         };
 
         self.run(exe_path.?, prog_node) catch {
@@ -272,7 +272,7 @@ const ZiglingStep = struct {
                 print("\n{s}Ziglings hint: {s}{s}", .{ bold_text, hint, reset_text });
 
             self.help();
-            std.os.exit(2);
+            std.process.exit(2);
         };
 
         // Print possible warning/debug messages.
@@ -281,14 +281,14 @@ const ZiglingStep = struct {
 
     fn run(self: *ZiglingStep, exe_path: []const u8, _: *std.Progress.Node) !void {
         resetLine();
-        print("Checking {s}...\n", .{self.exercise.main_file});
+        print("Checking: {s}\n", .{self.exercise.main_file});
 
         const b = self.step.owner;
 
         // Allow up to 1 MB of stdout capture.
         const max_output_bytes = 1 * 1024 * 1024;
 
-        var result = Child.exec(.{
+        const result = Child.run(.{
             .allocator = b.allocator,
             .argv = &.{exe_path},
             .cwd = b.build_root.path.?,
@@ -306,7 +306,7 @@ const ZiglingStep = struct {
         }
     }
 
-    fn check_output(self: *ZiglingStep, result: Child.ExecResult) !void {
+    fn check_output(self: *ZiglingStep, result: Child.RunResult) !void {
         const b = self.step.owner;
 
         // Make sure it exited cleanly.
@@ -355,7 +355,7 @@ const ZiglingStep = struct {
         print("{s}PASSED:\n{s}{s}\n\n", .{ green_text, output, reset_text });
     }
 
-    fn check_test(self: *ZiglingStep, result: Child.ExecResult) !void {
+    fn check_test(self: *ZiglingStep, result: Child.RunResult) !void {
         switch (result.term) {
             .Exited => |code| {
                 if (code != 0) {
@@ -376,7 +376,7 @@ const ZiglingStep = struct {
     }
 
     fn compile(self: *ZiglingStep, prog_node: *std.Progress.Node) !?[]const u8 {
-        print("Compiling {s}...\n", .{self.exercise.main_file});
+        print("Compiling: {s}\n", .{self.exercise.main_file});
 
         const b = self.step.owner;
         const exercise_path = self.exercise.main_file;
@@ -386,7 +386,7 @@ const ZiglingStep = struct {
         var zig_args = std.ArrayList([]const u8).init(b.allocator);
         defer zig_args.deinit();
 
-        zig_args.append(b.zig_exe) catch @panic("OOM");
+        zig_args.append(b.graph.zig_exe) catch @panic("OOM");
 
         const cmd = switch (self.exercise.kind) {
             .exe => "build-exe",
@@ -495,8 +495,7 @@ const PrintStep = struct {
     }
 
     fn make(step: *Step, _: *std.Progress.Node) !void {
-        const self = @fieldParentPtr(PrintStep, "step", step);
-
+        const self: *PrintStep = @alignCast(@fieldParentPtr("step", step));
         print("{s}", .{self.message});
     }
 };
@@ -839,7 +838,7 @@ const exercises = [_]Exercise{
     },
     .{
         .main_file = "060_floats.zig",
-        .output = "Shuttle liftoff weight: 1995796kg",
+        .output = "Shuttle liftoff weight: 2032092kg",
     },
     .{
         .main_file = "061_coercions.zig",
@@ -939,7 +938,7 @@ const exercises = [_]Exercise{
     .{
         .main_file = "082_anonymous_structs3.zig",
         .output =
-        \\"0"(bool):true "1"(bool):false "2"(i32):42 "3"(f32):3.14159202e+00
+        \\"0"(bool):true "1"(bool):false "2"(i32):42 "3"(f32):3.141592e0
         ,
         .hint = "This one is a challenge! But you have everything you need.",
     },
@@ -1103,6 +1102,35 @@ const exercises = [_]Exercise{
         \\This little poem has 15 words!
         ,
     },
+    .{
+        .main_file = "104_threading.zig",
+        .output =
+        \\Starting work...
+        \\thread 1: started.
+        \\thread 2: started.
+        \\thread 3: started.
+        \\Some weird stuff, after starting the threads.
+        \\thread 2: finished.
+        \\thread 1: finished.
+        \\thread 3: finished.
+        \\Zig is cool!
+        ,
+    },
+    .{
+        .main_file = "105_threading2.zig",
+        .output = "PI ≈ 3.14159265",
+    },
+    .{
+        .main_file = "106_files.zig",
+        .output = "Successfully wrote 18 bytes.",
+    },
+    .{
+        .main_file = "107_files2.zig",
+        .output =
+        \\AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+        \\Successfully Read 18 bytes: It's zigling time!
+        ,
+    },
     .{
         .main_file = "999_the_end.zig",
         .output =

ci/compat.sh

@@ -1,25 +0,0 @@
-#!/bin/bash
-# This script checks that `zig build` will return an useful error message when
-# the Zig compiler is not compatible, instead of failing due to a syntax error.
-#
-# This script should be run on an UNIX system.
-
-zig_version=$(zig version)
-
-zig build -Dn=1 -Dhealed &> /dev/null 2>&1
-zig_ret=$?
-
-if [ "$zig_ret" -eq 0 ]; then
-    printf "zig %s unexpectedly succeeded\n" "$zig_version"
-    exit 1
-fi
-
-zig_error=$(zig build -Dn=1 -Dhealed 2>&1)
-
-echo "$zig_error" | grep -q "it looks like your version of zig is too old"
-zig_ret=$?
-
-if [ "$zig_ret" -ne 0 ]; then
-    printf "zig %s is not compatible\n" "$zig_version"
-    exit 1
-fi

exercises/001_hello.zig

@@ -16,6 +16,6 @@
 //
 const std = @import("std");
 
-fn main() void {
+pub fn main() void {
     std.debug.print("Hello world!\n", .{});
 }

exercises/002_std.zig

@@ -11,7 +11,7 @@
 // Please complete the import below:
 //
 
-??? = @import("std");
+const std = @import("std");
 
 pub fn main() void {
     std.debug.print("Standard Library.\n", .{});

exercises/003_assignment.zig

@@ -34,12 +34,12 @@
 const std = @import("std");
 
 pub fn main() void {
-    const n: u8 = 50;
+    var n: u8 = 50;
     n = n + 5;
 
-    const pi: u8 = 314159;
+    const pi: u32 = 314159;
 
-    const negative_eleven: u8 = -11;
+    const negative_eleven: i8 = -11;
 
     // There are no errors in the next line, just explanation:
     // Perhaps you noticed before that the print function takes two

exercises/004_arrays.zig

@@ -27,7 +27,7 @@ pub fn main() void {
     // (Problem 1)
     // This "const" is going to cause a problem later - can you see what it is?
     // How do we fix it?
-    const some_primes = [_]u8{ 1, 3, 5, 7, 11, 13, 17, 19 };
+    var some_primes = [_]u8{ 1, 3, 5, 7, 11, 13, 17, 19 };
 
     // Individual values can be set with '[]' notation.
     // Example: This line changes the first prime to 2 (which is correct):
@@ -40,11 +40,11 @@ pub fn main() void {
     // (Problem 2)
     // Looks like we need to complete this expression. Use the example
     // above to set "fourth" to the fourth element of the some_primes array:
-    const fourth = some_primes[???];
+    const fourth = some_primes[3];
 
     // (Problem 3)
     // Use the len property to get the length of the array:
-    const length = some_primes.???;
+    const length = some_primes.len;
 
     std.debug.print("First: {}, Fourth: {}, Length: {}\n", .{
         first, fourth, length,

exercises/005_arrays2.zig

@@ -25,12 +25,12 @@ pub fn main() void {
     // (Problem 1)
     // Please set this array concatenating the two arrays above.
     // It should result in: 1 3 3 7
-    const leet = ???;
+    const leet = le ++ et;
 
     // (Problem 2)
     // Please set this array using repetition.
     // It should result in: 1 0 0 1 1 0 0 1 1 0 0 1
-    const bit_pattern = [_]u8{ ??? } ** 3;
+    const bit_pattern = [_]u8{ 1, 0, 0, 1 } ** 3;
 
     // Okay, that's all of the problems. Let's see the results.
     //

exercises/006_strings.zig

@@ -24,18 +24,18 @@ pub fn main() void {
     // (Problem 1)
     // Use array square bracket syntax to get the letter 'd' from
     // the string "stardust" above.
-    const d: u8 = ziggy[???];
+    const d: u8 = ziggy[4];
 
     // (Problem 2)
     // Use the array repeat '**' operator to make "ha ha ha ".
-    const laugh = "ha " ???;
+    const laugh = "ha " ** 3;
 
     // (Problem 3)
     // Use the array concatenation '++' operator to make "Major Tom".
     // (You'll need to add a space as well!)
     const major = "Major";
     const tom = "Tom";
-    const major_tom = major ??? tom;
+    const major_tom = major ++ " " ++ tom;
 
     // That's all the problems. Let's see our results:
     std.debug.print("d={u} {s}{s}\n", .{ d, laugh, major_tom });

exercises/007_strings2.zig

@@ -15,9 +15,9 @@ const std = @import("std");
 
 pub fn main() void {
     const lyrics =
-        Ziggy played guitar
-        Jamming good with Andrew Kelley
-        And the Spiders from Mars
+        \\Ziggy played guitar
+        \\Jamming good with Andrew Kelley
+        \\And the Spiders from Mars
     ;
 
     std.debug.print("{s}\n", .{lyrics});

exercises/008_quiz.zig

@@ -19,7 +19,7 @@ pub fn main() void {
     // the idiomatic type to use for array indexing.
     //
     // There IS a problem on this line, but 'usize' isn't it.
-    const x: usize = 1;
+    var x: usize = 1;
 
     // Note: When you want to declare memory (an array in this
     // case) without putting anything in it, you can set it to
@@ -33,10 +33,10 @@ pub fn main() void {
     lang[0] = letters[x];
 
     x = 3;
-    lang[???] = letters[x];
+    lang[1] = letters[x];
 
-    x = ???;
-    lang[2] = letters[???];
+    x = 5;
+    lang[2] = letters[x];
 
     // We want to "Program in Zig!" of course:
     std.debug.print("Program in {s}!\n", .{lang});

exercises/009_if.zig

@@ -24,7 +24,7 @@ pub fn main() void {
     const foo = 1;
 
     // Please fix this condition:
-    if (foo) {
+    if (foo == 1) {
         // We want our program to print this message!
         std.debug.print("Foo is 1!\n", .{});
     } else {

exercises/010_if2.zig

@@ -10,7 +10,7 @@ pub fn main() void {
 
     // Please use an if...else expression to set "price".
     // If discount is true, the price should be $17, otherwise $20:
-    const price: u8 = if ???;
+    const price: u8 = if (discount) 17 else 20;
 
     std.debug.print("With the discount, the price is ${}.\n", .{price});
 }

exercises/011_while.zig

@@ -21,7 +21,7 @@ pub fn main() void {
     var n: u32 = 2;
 
     // Please use a condition that is true UNTIL "n" reaches 1024:
-    while (???) {
+    while (n < 1024) {
         // Print the current number
         std.debug.print("{} ", .{n});
 

exercises/012_while2.zig

@@ -25,7 +25,7 @@ pub fn main() void {
 
     // Please set the continue expression so that we get the desired
     // results in the print statement below.
-    while (n < 1000) : ??? {
+    while (n < 1000) : (n *= 2) {
         // Print the current number
         std.debug.print("{} ", .{n});
     }

exercises/013_while3.zig

@@ -24,8 +24,8 @@ pub fn main() void {
     while (n <= 20) : (n += 1) {
         // The '%' symbol is the "modulo" operator and it
         // returns the remainder after division.
-        if (n % 3 == 0) ???;
-        if (n % 5 == 0) ???;
+        if (n % 3 == 0) continue;
+        if (n % 5 == 0) continue;
         std.debug.print("{} ", .{n});
     }
 

exercises/014_while4.zig

@@ -18,7 +18,7 @@ pub fn main() void {
     // Oh dear! This while loop will go forever?!
     // Please fix this so the print statement below gives the desired output.
     while (true) : (n += 1) {
-        if (???) ???;
+        if (n > 3) break;
     }
 
     // Result: we want n=4

exercises/015_for.zig

@@ -15,7 +15,7 @@ pub fn main() void {
 
     std.debug.print("A Dramatic Story: ", .{});
 
-    for (???) |???| {
+    for (story) |scene| {
         if (scene == 'h') std.debug.print(":-)  ", .{});
         if (scene == 's') std.debug.print(":-(  ", .{});
         if (scene == 'n') std.debug.print(":-|  ", .{});

exercises/016_for2.zig

@@ -25,7 +25,7 @@ pub fn main() void {
     // the value of the place as a power of two for each bit.
     //
     // See if you can figure out the missing pieces:
-    for (bits, ???) |bit, ???| {
+    for (bits, 0..) |bit, i| {
         // Note that we convert the usize i to a u32 with
         // @intCast(), a builtin function just like @import().
         // We'll learn about these properly in a later exercise.

exercises/017_quiz2.zig

@@ -9,18 +9,18 @@
 // Let's go from 1 to 16. This has been started for you, but there
 // are some problems. :-(
 //
-const std = import standard library;
+const std = @import("std");
 
-function main() void {
+pub fn main() void {
     var i: u8 = 1;
     const stop_at: u8 = 16;
 
     // What kind of loop is this? A 'for' or a 'while'?
-    ??? (i <= stop_at) : (i += 1) {
+    while (i <= stop_at) : (i += 1) {
         if (i % 3 == 0) std.debug.print("Fizz", .{});
         if (i % 5 == 0) std.debug.print("Buzz", .{});
         if (!(i % 3 == 0) and !(i % 5 == 0)) {
-            std.debug.print("{}", .{???});
+            std.debug.print("{}", .{i});
         }
         std.debug.print(", ", .{});
     }

exercises/018_functions.zig

@@ -25,6 +25,6 @@ pub fn main() void {
 // We're just missing a couple things. One thing we're NOT missing is the
 // keyword "pub", which is not needed here. Can you guess why?
 //
-??? deepThought() ??? {
+fn deepThought() u8 {
     return 42; // Number courtesy Douglas Adams
 }

exercises/019_functions2.zig

@@ -22,7 +22,7 @@ pub fn main() void {
 // You'll need to figure out the parameter name and type that we're
 // expecting. The output type has already been specified for you.
 //
-fn twoToThe(???) u32 {
+fn twoToThe(my_number: u8) u32 {
     return std.math.pow(u32, 2, my_number);
     // std.math.pow(type, a, b) takes a numeric type and two
     // numbers of that type (or that can coerce to that type) and

exercises/020_quiz3.zig

@@ -21,8 +21,8 @@ pub fn main() void {
 //
 // This function prints, but does not return anything.
 //
-fn printPowersOfTwo(numbers: [4]u16) ??? {
-    loop (numbers) |n| {
+fn printPowersOfTwo(numbers: [4]u16) void {
+    for (numbers) |n| {
         std.debug.print("{} ", .{twoToThe(n)});
     }
 }
@@ -31,13 +31,13 @@ fn printPowersOfTwo(numbers: [4]u16) ??? {
 // exercise. But don't be fooled! This one does the math without the aid
 // of the standard library!
 //
-fn twoToThe(number: u16) ??? {
+fn twoToThe(number: u16) u32 {
     var n: u16 = 0;
     var total: u16 = 1;
 
-    loop (n < number) : (n += 1) {
+    while (n < number) : (n += 1) {
         total *= 2;
     }
 
-    return ???;
+    return total;
 }

exercises/021_errors.zig

@@ -9,7 +9,7 @@
 // "TooSmall". Please add it where needed!
 const MyNumberError = error{
     TooBig,
-    ???,
+    TooSmall,
     TooFour,
 };
 
@@ -26,7 +26,7 @@ pub fn main() void {
         if (number_error == MyNumberError.TooBig) {
             std.debug.print(">4. ", .{});
         }
-        if (???) {
+        if (number_error == MyNumberError.TooSmall) {
             std.debug.print("<4. ", .{});
         }
         if (number_error == MyNumberError.TooFour) {

exercises/022_errors2.zig

@@ -19,7 +19,7 @@ const std = @import("std");
 const MyNumberError = error{TooSmall};
 
 pub fn main() void {
-    var my_number: ??? = 5;
+    var my_number: MyNumberError!u8 = 5;
 
     // Looks like my_number will need to either store a number OR
     // an error. Can you set the type correctly above?

exercises/023_errors3.zig

@@ -12,14 +12,14 @@ const MyNumberError = error{TooSmall};
 
 pub fn main() void {
     const a: u32 = addTwenty(44) catch 22;
-    const b: u32 = addTwenty(4) ??? 22;
+    const b: u32 = addTwenty(4) catch 22;
 
     std.debug.print("a={}, b={}\n", .{ a, b });
 }
 
 // Please provide the return type from this function.
 // Hint: it'll be an error union.
-fn addTwenty(n: u32) ??? {
+fn addTwenty(n: u32) MyNumberError!u32 {
     if (n < 5) {
         return MyNumberError.TooSmall;
     } else {

exercises/024_errors4.zig

@@ -59,7 +59,12 @@ fn fixTooSmall(n: u32) MyNumberError!u32 {
     // If we get a TooSmall error, we should return 10.
     // If we get any other error, we should return that error.
     // Otherwise, we return the u32 number.
-    return detectProblems(n) ???;
+    return detectProblems(n) catch |err| {
+        if (err == MyNumberError.TooSmall) {
+            return 10;
+        }
+        return err;
+    };
 }
 
 fn detectProblems(n: u32) MyNumberError!u32 {

exercises/025_errors5.zig

@@ -26,7 +26,7 @@ fn addFive(n: u32) MyNumberError!u32 {
     // This function needs to return any error which might come back from detect().
     // Please use a "try" statement rather than a "catch".
     //
-    var x = detect(n);
+    const x = try detect(n);
 
     return x + 5;
 }

exercises/026_hello2.zig

@@ -23,5 +23,5 @@ pub fn main() !void {
     // to be able to pass it up as a return value of main().
     //
     // We just learned of a single statement which can accomplish this.
-    stdout.print("Hello world!\n", .{});
+    try stdout.print("Hello world!\n", .{});
 }

exercises/027_defer.zig

@@ -20,6 +20,6 @@ const std = @import("std");
 pub fn main() void {
     // Without changing anything else, please add a 'defer' statement
     // to this code so that our program prints "One Two\n":
-    std.debug.print("Two\n", .{});
+    defer std.debug.print("Two\n", .{});
     std.debug.print("One ", .{});
 }

exercises/028_defer2.zig

@@ -18,7 +18,7 @@ pub fn main() void {
 fn printAnimal(animal: u8) void {
     std.debug.print("(", .{});
 
-    std.debug.print(") ", .{}); // <---- how?!
+    defer std.debug.print(") ", .{}); // <---- how?!
 
     if (animal == 'g') {
         std.debug.print("Goat", .{});

exercises/029_errdefer.zig

@@ -21,8 +21,8 @@ const MyErr = error{ GetFail, IncFail };
 
 pub fn main() void {
     // We simply quit the entire program if we fail to get a number:
-    var a: u32 = makeNumber() catch return;
-    var b: u32 = makeNumber() catch return;
+    const a: u32 = makeNumber() catch return;
+    const b: u32 = makeNumber() catch return;
 
     std.debug.print("Numbers: {}, {}\n", .{ a, b });
 }
@@ -32,7 +32,7 @@ fn makeNumber() MyErr!u32 {
 
     // Please make the "failed" message print ONLY if the makeNumber()
     // function exits with an error:
-    std.debug.print("failed!\n", .{});
+    errdefer std.debug.print("failed!\n", .{});
 
     var num = try getNumber(); // <-- This could fail!
 

exercises/030_switch.zig

@@ -46,6 +46,7 @@ pub fn main() void {
             // match for every possible value).  Please add an "else"
             // to this switch to print a question mark "?" when c is
             // not one of the existing matches.
+            else => std.debug.print("?", .{}),
         }
     }
 

exercises/031_switch2.zig

@@ -31,6 +31,7 @@ pub fn main() void {
             26 => 'Z',
             // As in the last exercise, please add the 'else' clause
             // and this time, have it return an exclamation mark '!'.
+            else => '!',
         };
 
         std.debug.print("{c}", .{real_char});

exercises/032_unreachable.zig

@@ -35,6 +35,7 @@ pub fn main() void {
             3 => {
                 current_value *= current_value;
             },
+            else => unreachable,
         }
 
         std.debug.print("{} ", .{current_value});

exercises/033_iferror.zig

@@ -39,7 +39,7 @@ pub fn main() void {
             std.debug.print("={}. ", .{value});
         } else |err| switch (err) {
             MyNumberError.TooBig => std.debug.print(">4. ", .{}),
-            // Please add a match for TooSmall here and have it print: "<4. "
+            MyNumberError.TooSmall => std.debug.print("<4. ", .{}),
         }
     }
 

exercises/034_quiz4.zig

@@ -6,14 +6,11 @@
 //     my_num=42
 //
 const std = @import("std");
-
 const NumError = error{IllegalNumber};
 
-pub fn main() void {
+pub fn main() !void {
     const stdout = std.io.getStdOut().writer();
-
-    const my_num: u32 = getNumber();
-
+    const my_num: u32 = try getNumber();
     try stdout.print("my_num={}\n", .{my_num});
 }
 

exercises/035_enums.zig

@@ -20,7 +20,7 @@
 const std = @import("std");
 
 // Please complete the enum!
-const Ops = enum { ??? };
+const Ops = enum { inc, dec, pow };
 
 pub fn main() void {
     const operations = [_]Ops{

exercises/036_enums2.zig

@@ -31,7 +31,7 @@ const std = @import("std");
 const Color = enum(u32) {
     red = 0xff0000,
     green = 0x00ff00,
-    blue = ???,
+    blue = 0x0000ff,
 };
 
 pub fn main() void {
@@ -53,12 +53,12 @@ pub fn main() void {
         \\<p>
         \\  <span style="color: #{x:0>6}">Red</span>
         \\  <span style="color: #{x:0>6}">Green</span>
-        \\  <span style="color: #{}">Blue</span>
+        \\  <span style="color: #{x:0>6}">Blue</span>
         \\</p>
         \\
     , .{
         @intFromEnum(Color.red),
         @intFromEnum(Color.green),
-        @intFromEnum(???), // Oops! We're missing something!
+        @intFromEnum(Color.blue), // Oops! We're missing something!
     });
 }

exercises/039_pointers.zig

@@ -24,7 +24,7 @@ const std = @import("std");
 
 pub fn main() void {
     var num1: u8 = 5;
-    var num1_pointer: *u8 = &num1;
+    const num1_pointer: *u8 = &num1;
 
     var num2: u8 = undefined;
 

exercises/046_optionals2.zig

@@ -51,8 +51,6 @@ fn visitElephants(first_elephant: *Elephant) void {
         // We should stop once we encounter a tail that
         // does NOT point to another element. What can
         // we put here to make that happen?
-        if (e.tail == null) ???;
-
-        e = e.tail.?;
+        e = e.tail ???
     }
 }

exercises/048_methods2.zig

@@ -24,7 +24,7 @@ const Elephant = struct {
 
     pub fn print(self: *Elephant) void {
         // Prints elephant letter and [v]isited
-        var v: u8 = if (self.visited) 'v' else ' ';
+        const v: u8 = if (self.visited) 'v' else ' ';
         std.debug.print("{u}{u} ", .{ self.letter, v });
     }
 };

exercises/049_quiz6.zig

@@ -37,7 +37,7 @@ const Elephant = struct {
 
     pub fn print(self: *Elephant) void {
         // Prints elephant letter and [v]isited
-        var v: u8 = if (self.visited) 'v' else ' ';
+        const v: u8 = if (self.visited) 'v' else ' ';
         std.debug.print("{u}{u} ", .{ self.letter, v });
     }
 };

exercises/051_values.zig

@@ -141,9 +141,20 @@ pub fn main() void {
     //
     // Moving along...
     //
-    // Passing arguments to functions is pretty much exactly like
-    // making an assignment to a const (since Zig enforces that ALL
-    // function parameters are const).
+    // When arguments are passed to a function,
+    // they are ALWAYS passed as constants within the function,
+    // regardless of how they were declared in the calling function.
+    //
+    // Example:
+    // fn foo(arg: u8) void {
+    //    arg = 42; // Error, 'arg' is const!
+    // }
+    //
+    // fn bar() void {
+    //    var arg: u8 = 12;
+    //    foo(arg);
+    //    ...
+    // }
     //
     // Knowing this, see if you can make levelUp() work as expected -
     // it should add the specified amount to the supplied character's

exercises/055_unions.zig

@@ -53,8 +53,8 @@ const AntOrBee = enum { a, b };
 
 pub fn main() void {
     // We'll just make one bee and one ant to test them out:
-    var ant = Insect{ .still_alive = true };
-    var bee = Insect{ .flowers_visited = 15 };
+    const ant = Insect{ .still_alive = true };
+    const bee = Insect{ .flowers_visited = 15 };
 
     std.debug.print("Insect report! ", .{});
 

exercises/056_unions2.zig

@@ -38,8 +38,8 @@ const Insect = union(InsectStat) {
 };
 
 pub fn main() void {
-    var ant = Insect{ .still_alive = true };
-    var bee = Insect{ .flowers_visited = 16 };
+    const ant = Insect{ .still_alive = true };
+    const bee = Insect{ .flowers_visited = 16 };
 
     std.debug.print("Insect report! ", .{});
 

exercises/057_unions3.zig

@@ -21,8 +21,8 @@ const Insect = union(InsectStat) {
 };
 
 pub fn main() void {
-    var ant = Insect{ .still_alive = true };
-    var bee = Insect{ .flowers_visited = 17 };
+    const ant = Insect{ .still_alive = true };
+    const bee = Insect{ .flowers_visited = 17 };
 
     std.debug.print("Insect report! ", .{});
 

exercises/058_quiz7.zig

@@ -273,7 +273,7 @@ const HermitsNotebook = struct {
     // distance) than the one we'd noted before. If it is, we
     // overwrite the old entry with the new one.
     fn checkNote(self: *HermitsNotebook, note: NotebookEntry) void {
-        var existing_entry = self.getEntry(note.place);
+        const existing_entry = self.getEntry(note.place);
 
         if (existing_entry == null) {
             self.entries[self.end_of_entries] = note;
@@ -386,7 +386,7 @@ pub fn main() void {
     // "start" entry we just added) until we run out, at which point
     // we'll have checked every reachable Place.
     while (notebook.hasNextEntry()) {
-        var place_entry = notebook.getNextEntry();
+        const place_entry = notebook.getNextEntry();
 
         // For every Path that leads FROM the current Place, create a
         // new note (in the form of a NotebookEntry) with the

exercises/059_integers.zig

@@ -2,12 +2,12 @@
 // Zig lets you express integer literals in several convenient
 // formats. These are all the same value:
 //
-//     const a1: u8 = 65;        // decimal
-//     const a2: u8 = 0x41;      // hexadecimal
-//     const a3: u8 = 0o101;     // octal
-//     const a4: u8 = 0b1000001; // binary
-//     const a5: u8 = 'A';       // ASCII code point literal
-//     const a6: u16 = 'Ȁ';      // Unicode code points can take up to 21 bits
+//     const a1: u8 = 65;          // decimal
+//     const a2: u8 = 0x41;        // hexadecimal
+//     const a3: u8 = 0o101;       // octal
+//     const a4: u8 = 0b1000001;   // binary
+//     const a5: u8 = 'A';         // ASCII code point literal
+//     const a6: u16 = '\u{0041}'; // Unicode code points can take up to 21 bits
 //
 // You can also place underscores in numbers to aid readability:
 //

exercises/060_floats.zig

@@ -39,11 +39,11 @@ const print = @import("std").debug.print;
 
 pub fn main() void {
     // The approximate weight of the Space Shuttle upon liftoff
-    // (including boosters and fuel tank) was 2,200 tons.
+    // (including boosters and fuel tank) was 4,480,000 lb.
     //
-    // We'll convert this weight from tons to kilograms at a
-    // conversion of 907.18kg to the ton.
-    const shuttle_weight: f16 = 907.18 * 2200;
+    // We'll convert this weight from pound to kilograms at a
+    // conversion of 0.453592kg to the pound.
+    const shuttle_weight: f16 = 0.453592 * 4480e6;
 
     // By default, float values are formatted in scientific
     // notation. Try experimenting with '{d}' and '{d:.3}' to see

exercises/064_builtins.zig

@@ -58,7 +58,7 @@ pub fn main() void {
     // There is a difference between
     //  - a value, that overflowed at some point and is now corrupted
     //  - a single operation that overflows and maybe causes subsequent errors
-    // In practise we usually notice the overflowed value first and have to work
+    // In practice we usually notice the overflowed value first and have to work
     // our way backwards to the operation that caused the overflow.
     //
     // If there was no overflow at all while adding 5 to a, what value would

exercises/067_comptime2.zig

@@ -38,16 +38,16 @@ pub fn main() void {
     var count = 0;
 
     count += 1;
-    var a1: [count]u8 = .{'A'} ** count;
+    const a1: [count]u8 = .{'A'} ** count;
 
     count += 1;
-    var a2: [count]u8 = .{'B'} ** count;
+    const a2: [count]u8 = .{'B'} ** count;
 
     count += 1;
-    var a3: [count]u8 = .{'C'} ** count;
+    const a3: [count]u8 = .{'C'} ** count;
 
     count += 1;
-    var a4: [count]u8 = .{'D'} ** count;
+    const a4: [count]u8 = .{'D'} ** count;
 
     print("{s} {s} {s} {s}\n", .{ a1, a2, a3, a4 });
 

exercises/070_comptime5.zig

@@ -83,19 +83,19 @@ const DuctError = error{UnmatchedDiameters};
 
 pub fn main() void {
     // This is a real duck!
-    var ducky1 = Duck{
+    const ducky1 = Duck{
         .eggs = 0,
         .loudness = 3,
     };
 
     // This is not a real duck, but it has quack() and waddle()
     // abilities, so it's still a "duck".
-    var ducky2 = RubberDuck{
+    const ducky2 = RubberDuck{
         .in_bath = false,
     };
 
     // This is not even remotely a duck.
-    var ducky3 = Duct{
+    const ducky3 = Duct{
         .diameter = 17,
         .length = 165,
         .galvanized = true,

exercises/072_comptime7.zig

@@ -39,7 +39,7 @@ pub fn main() void {
 
         // This gets the digit from the "instruction". Can you
         // figure out why we subtract '0' from it?
-        comptime var digit = instructions[i + 1] - '0';
+        const digit = instructions[i + 1] - '0';
 
         // This 'switch' statement contains the actual work done
         // at runtime. At first, this doesn't seem exciting...

exercises/075_quiz8.zig

@@ -110,7 +110,7 @@ const HermitsNotebook = struct {
     }
 
     fn checkNote(self: *HermitsNotebook, note: NotebookEntry) void {
-        var existing_entry = self.getEntry(note.place);
+        const existing_entry = self.getEntry(note.place);
 
         if (existing_entry == null) {
             self.entries[self.end_of_entries] = note;
@@ -180,7 +180,7 @@ pub fn main() void {
     notebook.checkNote(working_note);
 
     while (notebook.hasNextEntry()) {
-        var place_entry = notebook.getNextEntry();
+        const place_entry = notebook.getNextEntry();
 
         for (place_entry.place.paths) |*path| {
             working_note = NotebookEntry{

exercises/076_sentinels.zig

@@ -46,7 +46,7 @@ pub fn main() void {
     var nums = [_:0]u32{ 1, 2, 3, 4, 5, 6 };
 
     // And here's a zero-terminated many-item pointer:
-    var ptr: [*:0]u32 = &nums;
+    const ptr: [*:0]u32 = &nums;
 
     // For fun, let's replace the value at position 3 with the
     // sentinel value 0. This seems kind of naughty.
@@ -74,8 +74,8 @@ pub fn main() void {
 fn printSequence(my_seq: anytype) void {
     const my_typeinfo = @typeInfo(@TypeOf(my_seq));
 
-    // The TypeInfo contained in my_type is a union. We use a
-    // switch to handle printing the Array or Pointer fields,
+    // The TypeInfo contained in my_typeinfo is a union. We use
+    // a switch to handle printing the Array or Pointer fields,
     // depending on which type of my_seq was passed in:
     switch (my_typeinfo) {
         .Array => {

exercises/080_anonymous_structs.zig

@@ -48,13 +48,13 @@ pub fn main() void {
     // * circle1 should hold i32 integers
     // * circle2 should hold f32 floats
     //
-    var circle1 = ??? {
+    const circle1 = ??? {
         .center_x = 25,
         .center_y = 70,
         .radius = 15,
     };
 
-    var circle2 = ??? {
+    const circle2 = ??? {
         .center_x = 25.234,
         .center_y = 70.999,
         .radius = 15.714,

exercises/092_interfaces.zig

@@ -96,7 +96,7 @@ const Insect = union(enum) {
 };
 
 pub fn main() !void {
-    var my_insects = [_]Insect{
+    const my_insects = [_]Insect{
         Insect{ .ant = Ant{ .still_alive = true } },
         Insect{ .bee = Bee{ .flowers_visited = 17 } },
         Insect{ .grasshopper = Grasshopper{ .distance_hopped = 32 } },

exercises/093_hello_c.zig

@@ -40,7 +40,7 @@
 // our well-known "import" for Zig
 const std = @import("std");
 
-// and here the new the import for C
+// and here the new import for C
 const c = @cImport({
     @cInclude("unistd.h");
 });

exercises/094_c_math.zig

@@ -1,19 +1,26 @@
 //
 // Often, C functions are used where no equivalent Zig function exists
-// yet. Since the integration of a C function is very simple, as already
+// yet. Okay, that's getting less and less. ;-)
+//
+// Since the integration of a C function is very simple, as already
 // seen in the last exercise, it naturally offers itself to use the
 // very large variety of C functions for our own programs.
 // As an example:
 //
 // Let's say we have a given angle of 765.2 degrees. If we want to
 // normalize that, it means that we have to subtract X * 360 degrees
-// to get the correct angle. How could we do that? A good method is
-// to use the modulo function. But if we write "765.2 % 360", it won't
-// work, because the standard modulo function works only with integer
-// values. In the C library "math", there is a function called "fmod";
-// the "f" stands for floating and means that we can solve modulo for
-// real numbers. With this function, it should be possible to normalize
-// our angle. Let's go.
+// to get the correct angle.
+// How could we do that? A good method is to use the modulo function.
+// But if we write "765.2 % 360", it only works with float values
+// that are known at compile time.
+// In Zig, we would use @mod(a, b) instead.
+//
+// Let us now assume that we cannot do this in Zig, but only with
+// a C function from the standard library. In the library "math",
+// there is a function called "fmod"; the "f" stands for floating
+// and means that we can solve modulo for real numbers. With this
+// function, it should be possible to normalize our angle.
+// Let's go.
 
 const std = @import("std");
 

exercises/096_memory_allocation.zig

@@ -30,9 +30,9 @@
 //         std.debug.print("slice_ptr={*}\n", .{slice_ptr});
 //     }
 
-// Instead of a simple integer or a constant sized slice, this
-// program requires a slice to be allocated that is the same size as
-// an input array.
+// Instead of a simple integer or a slice with a constant size,
+// this program requires allocating a slice that is the same size
+// as an input array.
 
 // Given a series of numbers, take the running average. In other
 // words, each item N should contain the average of the last N
@@ -52,7 +52,7 @@ fn runningAverage(arr: []const f64, avg: []f64) void {
 
 pub fn main() !void {
     // pretend this was defined by reading in user input
-    var arr: []const f64 = &[_]f64{ 0.3, 0.2, 0.1, 0.1, 0.4 };
+    const arr: []const f64 = &[_]f64{ 0.3, 0.2, 0.1, 0.1, 0.4 };
 
     // initialize the allocator
     var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
@@ -64,7 +64,7 @@ pub fn main() !void {
     const allocator = arena.allocator();
 
     // allocate memory for this array
-    var avg: []f64 = ???;
+    const avg: []f64 = ???;
 
     runningAverage(arr, avg);
     std.debug.print("Running Average: ", .{});

exercises/097_bit_manipulation.zig

@@ -1,5 +1,5 @@
 //
-// Bit manipulations is a very powerful tool just also from Zig.
+// Bit manipulation is a very powerful tool, also from Zig.
 // Since the dawn of the computer age, numerous algorithms have been
 // developed that solve tasks solely by moving, setting, or logically
 // combining bits.
@@ -8,10 +8,10 @@
 // functions where possible. And it is often possible with calculations
 // based on integers.
 //
-// Often it is not easy to understand at first glance what exactly these
+// At first glance, it is often not easy to understand what exactly these
 // algorithms do when only "numbers" in memory areas change outwardly.
-// But it must never be forgotten that the numbers only represent the
-// interpretation of the bit sequences.
+// However, it should never be forgotten that the numbers only represent
+// the interpretation of the bit sequences.
 //
 // Quasi the reversed case we have otherwise, namely that we represent
 // numbers in bit sequences.
@@ -20,8 +20,8 @@
 //
 // Zig provides all the necessary functions to change the bits inside
 // a variable. It is distinguished whether the bit change leads to an
-// overflow or not.The details are in the Zig documentation in section
-// 10.1 "Table of Operators".
+// overflow or not. The details are in the Zig documentation in section
+// "Table of Operators".
 //
 // Here are some examples of how the bits of variables can be changed:
 //

exercises/098_bit_manipulation2.zig

@@ -1,5 +1,5 @@
 //
-// Another useful practice for bit manipulation is setting bits as flags.
+// Another useful application for bit manipulation is setting bits as flags.
 // This is especially useful when processing lists of something and storing
 // the states of the entries, e.g. a list of numbers and for each prime
 // number a flag is set.
@@ -19,9 +19,9 @@
 // For example, you could take an array of bool and set the value to 'true'
 // for each letter in the order of the alphabet (a=0; b=1; etc.) found in
 // the sentence. However, this is neither memory efficient nor particularly
-// fast. Instead we take a simpler way, very similar in principle, we define
-// a variable with at least 26 bits (e.g. u32) and also set the bit for each
-// letter found at the corresponding position.
+// fast. Instead we choose a simpler approach that is very similar in principle:
+// We define a variable with at least 26 bits (e.g. u32) and set the bit for
+// each letter that is found in the corresponding position.
 //
 // Zig provides functions for this in the standard library, but we prefer to
 // solve it without these extras, after all we want to learn something.
@@ -39,7 +39,7 @@ fn isPangram(str: []const u8) bool {
     // first we check if the string has at least 26 characters
     if (str.len < 26) return false;
 
-    // we uses a 32 bit variable of which we need 26 bits
+    // we use a 32 bit variable of which we need 26 bits
     var bits: u32 = 0;
 
     // loop about all characters in the string
@@ -49,7 +49,7 @@ fn isPangram(str: []const u8) bool {
             // then we set the bit at the position
             //
             // to do this, we use a little trick:
-            // since the letters in the ASCI table start at 65
+            // since the letters in the ASCII table start at 65
             // and are numbered sequentially, we simply subtract the
             // first letter (in this case the 'a') from the character
             // found, and thus get the position of the desired bit

exercises/099_formatting.zig

@@ -19,10 +19,10 @@
 //     https://github.com/ziglang/zig/blob/master/lib/std/fmt.zig#L29
 //
 // Zig already has a very nice selection of formatting options.
-// These can be used in different ways, but typically to convert
-// numerical values into various text representations. The
-// results can be used for direct output to a terminal or stored
-// for later use or written to a file. The latter is useful when
+// These can be used in different ways, but generally to convert
+// numerical values into various text representations. The results
+// can be used for direct output to a terminal or stored for
+// later use or written to a file. The latter is useful when
 // large amounts of data are to be processed by other programs.
 //
 // In Ziglings, we are concerned with the output to the console.

exercises/103_tokenization.zig

@@ -1,9 +1,9 @@
 //
 // The functionality of the standard library is becoming increasingly
-// important in Zig. On the one hand, it is helpful to look at how
+// important in Zig. First of all, it is helpful to take a look at how
 // the individual functions are implemented. Because this is wonderfully
-// suitable as a template for your own functions. On the other hand,
-// these standard functions are part of the basic equipment of Zig.
+// suitable as a template for your own functions. In addition these
+// standard functions are part of the basic configuration of Zig.
 //
 // This means that they are always available on every system.
 // Therefore it is worthwhile to deal with them also in Ziglings.

exercises/104_threading.zig

@@ -0,0 +1,134 @@
+//
+// Whenever there is a lot to calculate, the question arises as to how
+// tasks can be carried out simultaneously. We have already learned about
+// one possibility, namely asynchronous processes, in Exercises 84-91.
+//
+// However, the computing power of the processor is only distributed to
+// the started and running tasks, which always reaches its limits when
+// pure computing power is called up.
+//
+// For example, in blockchains based on proof of work, the miners have
+// to find a nonce for a certain character string so that the first m bits
+// in the hash of the character string and the nonce are zeros.
+// As the miner who can solve the task first receives the reward, everyone
+// tries to complete the calculations as quickly as possible.
+//
+// This is where multithreading comes into play, where tasks are actually
+// distributed across several cores of the CPU or GPU, which then really
+// means a multiplication of performance.
+//
+// The following diagram roughly illustrates the difference between the
+// various types of process execution.
+// The 'Overall Time' column is intended to illustrate how the time is
+// affected if, instead of one core as in synchronous and asynchronous
+// processing, a second core now helps to complete the work in multithreading.
+//
+// In the ideal case shown, execution takes only half the time compared
+// to the synchronous single thread. And even asynchronous processing
+// is only slightly faster in comparison.
+//
+//
+// Synchronous  Asynchronous
+// Processing   Processing        Multithreading
+// ┌──────────┐ ┌──────────┐  ┌──────────┐ ┌──────────┐
+// │ Thread 1 │ │ Thread 1 │  │ Thread 1 │ │ Thread 2 │
+// ├──────────┤ ├──────────┤  ├──────────┤ ├──────────┤    Overall Time
+// └──┼┼┼┼┼───┴─┴──┼┼┼┼┼───┴──┴──┼┼┼┼┼───┴─┴──┼┼┼┼┼───┴──┬───────┬───────┬──
+//    ├───┤        ├───┤         ├───┤        ├───┤      │       │       │
+//    │ T │        │ T │         │ T │        │ T │      │       │       │
+//    │ a │        │ a │         │ a │        │ a │      │       │       │
+//    │ s │        │ s │         │ s │        │ s │      │       │       │
+//    │ k │        │ k │         │ k │        │ k │      │       │       │
+//    │   │        │   │         │   │        │   │      │       │       │
+//    │ 1 │        │ 1 │         │ 1 │        │ 3 │      │       │       │
+//    └─┬─┘        └─┬─┘         └─┬─┘        └─┬─┘      │       │       │
+//      │            │             │            │      5 Sec     │       │
+// ┌────┴───┐      ┌─┴─┐         ┌─┴─┐        ┌─┴─┐      │       │       │
+// │Blocking│      │ T │         │ T │        │ T │      │       │       │
+// └────┬───┘      │ a │         │ a │        │ a │      │       │       │
+//      │          │ s │         │ s │        │ s │      │     8 Sec     │
+//    ┌─┴─┐        │ k │         │ k │        │ k │      │       │       │
+//    │ T │        │   │         │   │        │   │      │       │       │
+//    │ a │        │ 2 │         │ 2 │        │ 4 │      │       │       │
+//    │ s │        └─┬─┘         ├───┤        ├───┤      │       │       │
+//    │ k │          │           │┼┼┼│        │┼┼┼│      ▼       │    10 Sec
+//    │   │        ┌─┴─┐         └───┴────────┴───┴─────────     │       │
+//    │ 1 │        │ T │                                         │       │
+//    └─┬─┘        │ a │                                         │       │
+//      │          │ s │                                         │       │
+//    ┌─┴─┐        │ k │                                         │       │
+//    │ T │        │   │                                         │       │
+//    │ a │        │ 1 │                                         │       │
+//    │ s │        ├───┤                                         │       │
+//    │ k │        │┼┼┼│                                         ▼       │
+//    │   │        └───┴────────────────────────────────────────────     │
+//    │ 2 │                                                              │
+//    ├───┤                                                              │
+//    │┼┼┼│                                                              ▼
+//    └───┴────────────────────────────────────────────────────────────────
+//
+//
+// The diagram was modeled on the one in a blog in which the differences
+// between asynchronous processing and multithreading are explained in detail:
+// https://blog.devgenius.io/multi-threading-vs-asynchronous-programming-what-is-the-difference-3ebfe1179a5
+//
+// Our exercise is essentially about clarifying the approach in Zig and
+// therefore we try to keep it as simple as possible.
+// Multithreading in itself is already difficult enough. ;-)
+//
+const std = @import("std");
+
+pub fn main() !void {
+    // This is where the preparatory work takes place
+    // before the parallel processing begins.
+    std.debug.print("Starting work...\n", .{});
+
+    // These curly brackets are very important, they are necessary
+    // to enclose the area where the threads are called.
+    // Without these brackets, the program would not wait for the
+    // end of the threads and they would continue to run beyond the
+    // end of the program.
+    {
+        // Now we start the first thread, with the number as parameter
+        const handle = try std.Thread.spawn(.{}, thread_function, .{1});
+
+        // Waits for the thread to complete,
+        // then deallocates any resources created on `spawn()`.
+        defer handle.join();
+
+        // Second thread
+        const handle2 = try std.Thread.spawn(.{}, thread_function, .{-4}); // that can't be right?
+        defer handle2.join();
+
+        // Third thread
+        const handle3 = try std.Thread.spawn(.{}, thread_function, .{3});
+        defer ??? // <-- something is missing
+
+        // After the threads have been started,
+        // they run in parallel and we can still do some work in between.
+        std.time.sleep(1500 * std.time.ns_per_ms);
+        std.debug.print("Some weird stuff, after starting the threads.\n", .{});
+    }
+    // After we have left the closed area, we wait until
+    // the threads have run through, if this has not yet been the case.
+    std.debug.print("Zig is cool!\n", .{});
+}
+
+// This function is started with every thread that we set up.
+// In our example, we pass the number of the thread as a parameter.
+fn thread_function(num: usize) !void {
+    std.time.sleep(200 * num * std.time.ns_per_ms);
+    std.debug.print("thread {d}: {s}\n", .{ num, "started." });
+
+    // This timer simulates the work of the thread.
+    const work_time = 3 * ((5 - num % 3) - 2);
+    std.time.sleep(work_time * std.time.ns_per_s);
+
+    std.debug.print("thread {d}: {s}\n", .{ num, "finished." });
+}
+// This is the easiest way to run threads in parallel.
+// In general, however, more management effort is required,
+// e.g. by setting up a pool and allowing the threads to communicate
+// with each other using semaphores.
+//
+// But that's a topic for another exercise.

exercises/105_threading2.zig

@@ -0,0 +1,107 @@
+//
+// Now that we are familiar with the principles of multi-threading,
+// let's boldly venture into a practical example from mathematics.
+// We will determine the circle number PI with sufficient accuracy.
+//
+// There are different methods for this, and some of them are several
+// hundred years old. For us, the dusty procedures are surprisingly well
+// suited to our exercise. Because the mathematicians of the time didn't
+// have fancy computers with which we can calculate something like this
+// in seconds today.
+// Whereby, of course, it depends on the accuracy, i.e. how many digits
+// after the decimal point we are interested in.
+// But these old procedures can still be tackled with paper and pencil,
+// which is why they are easier for us to understand.
+// At least for me. ;-)
+//
+// So let's take a mental leap back a few years.
+// Around 1672 (if you want to know and read about it in detail, you can
+// do so on Wikipedia, for example), various mathematicians once again
+// discovered a method of approaching the circle number PI.
+// There were the Scottish mathematician Gregory and the German
+// mathematician Leibniz, and even a few hundred years earlier the Indian
+// mathematician Madhava. All of them independently developed the same
+// formula, which was published by Leibnitz in 1682 in the journal
+// "Acta Eruditorum".
+// This is why this method has become known as the "Leibnitz series",
+// although the other names are also often used today.
+// We will not go into the formula and its derivation in detail, but
+// will deal with the series straight away:
+//
+//        4     4     4     4     4
+//  PI = --- - --- + --- - --- + --- ...
+//        1     3     5     7     9
+//
+// As you can clearly see, the series starts with the whole number 4 and
+// approaches the circle number by subtracting and adding smaller and
+// smaller parts of 4. Pretty much everyone has learned PI = 3.14 at school,
+// but very few people remember other digits, and this is rarely necessary
+// in practice. Because either you don't need the precision, or you use a
+// calculator in which the number is stored as a very precise constant.
+// But at some point this constant was calculated and we are doing the same
+// now.The question at this point is, how many partial values do we have
+// to calculate for which accuracy?
+//
+// The answer is chewing, to get 8 digits after the decimal point we need
+// 1,000,000,000 partial values. And for each additional digit we have to
+// add a zero.
+// Even fast computers - and I mean really fast computers - get a bit warmer
+// on the CPU when it comes to really many digits. But the 8 digits are
+// enough for us for now, because we want to understand the principle and
+// nothing more, right?
+//
+// As we have already discovered, the Leibnitz series is a series with a
+// fixed distance of 2 between the individual partial values. This makes
+// it easy to apply a simple loop to it, because if we start with n = 1
+// (which is not necessarily useful now) we always have to add 2 in each
+// round.
+// But wait! The partial values are alternately added and subtracted.
+// This could also be achieved with one loop, but not very elegantly.
+// It also makes sense to split this between two CPUs, one calculates
+// the positive values and the other the negative values. And so we can
+// simply start two threads and add everything up at the end and we're
+// done.
+// We just have to remember that if only the positive or negative values
+// are calculated, the distances are twice as large, i.e. 4.
+//
+// So that the whole thing has a real learning effect, the first thread
+// call is specified and you have to make the second.
+// But don't worry, it will work out. :-)
+//
+const std = @import("std");
+
+pub fn main() !void {
+    const count = 1_000_000_000;
+    var pi_plus: f64 = 0;
+    var pi_minus: f64 = 0;
+
+    {
+        // First thread to calculate the plus numbers.
+        const handle1 = try std.Thread.spawn(.{}, thread_pi, .{ &pi_plus, 5, count });
+        defer handle1.join();
+
+        // Second thread to calculate the minus numbers.
+        ???
+        
+    }
+    // Here we add up the results.
+    std.debug.print("PI ≈ {d:.8}\n", .{4 + pi_plus - pi_minus});
+}
+
+fn thread_pi(pi: *f64, begin: u64, end: u64) !void {
+    var n: u64 = begin;
+    while (n < end) : (n += 4) {
+        pi.* += 4 / @as(f64, @floatFromInt(n));
+    }
+}
+// If you wish, you can increase the number of loop passes, which
+// improves the number of digits.
+//
+// But be careful:
+// In order for parallel processing to really show its strengths,
+// the compiler must be given the "-O ReleaseFast" flag when it
+// is created. Otherwise the debug functions slow down the speed
+// to such an extent that seconds become minutes during execution.
+//
+// And you should remove the formatting restriction in "print",
+// otherwise you will not be able to see the additional digits.

exercises/106_files.zig

@@ -0,0 +1,92 @@
+//
+// Until now, we've only been printing our output in the console,
+// which is good enough for fighting alien and hermit bookkeeping.
+//
+// However, many other task require some interaction with the file system,
+// which is the underlying structure for organizing files on your computer.
+//
+// The File System provide a hierarchical structure for storing files
+// by organizing files into directories, which hold files and other directories,
+// thus creating a tree structure for navigating.
+//
+// Fortunately, zig standard library provide a simple api for interacting
+// with the file system, see the detail documentation here
+//
+// https://ziglang.org/documentation/master/std/#std.fs
+//
+// In this exercise, we'll try to
+//   - create a new directory
+//   - open a file in the directory
+//   - write to the file.
+//
+// import std as always
+const std = @import("std");
+
+pub fn main() !void {
+    // first we get the current working directory
+    const cwd: std.fs.Dir = std.fs.cwd();
+
+    // then we'll try to make a new directory /output/
+    // to put our output files.
+    cwd.makeDir("output") catch |e| switch (e) {
+        // there are chance you might want to run this
+        // program more than once and the path might already
+        // been created, so we'll have to handle this error
+        // by doing nothing
+        //
+        // we want to catch error.PathAlreadyExists and do nothing
+        ??? => {},
+        // if is any other unexpected error we just propagate it through
+        else => return e,
+    };
+
+    // then we'll try to open our freshly created directory
+    // wait a minute
+    // opening a directory might fail!
+    // what should we do here?
+    var output_dir: std.fs.Dir = cwd.openDir("output", .{});
+    defer output_dir.close();
+
+    // we try to open the file `zigling.txt`,
+    // and propagate the error up if there are any errors
+    const file: std.fs.File = try output_dir.createFile("zigling.txt", .{});
+    // it is a good habit to close a file after you are done with it
+    // so that other programs can read it and prevent data corruption
+    // but here we are not yet done writing to the file
+    // if only there were a keyword in zig that
+    // allows you "defer" code execute to the end of scope...
+    file.close();
+
+    // !you are not allowed to switch these two lines above the file closing line!
+    const byte_written = try file.write("It's zigling time!");
+    std.debug.print("Successfully wrote {d} bytes.\n", .{byte_written});
+}
+// to check if you actually write to the file, you can either,
+// 1. open the file on your text editor, or
+// 2. print the content of the file in the console with the following command
+//    >> cat ./output/zigling.txt
+//
+//
+// More on Creating files
+//
+// notice in:
+// ... try output_dir.createFile("zigling.txt", .{});
+//                                              ^^^
+//                 we passed this anonymous struct to the function call
+//
+// this is the struct `CreateFlag` with default fields
+// {
+//      read: bool = false,
+//      truncate: bool = true,
+//      exclusive: bool = false,
+//      lock: Lock = .none,
+//      lock_nonblocking: bool = false,
+//      mode: Mode = default_mode
+// }
+//
+// Question:
+//   - what should you do if you want to also read the file after opening it?
+//   - go to documentation of the struct `std.fs.Dir` here
+//     https://ziglang.org/documentation/master/std/#std.fs.Dir
+//       - can you find a function for opening a file? how about deleting a file?
+//       - what kind of options can you use with those functions?

exercises/107_files2.zig

@@ -0,0 +1,52 @@
+//
+// Prerequisite :
+//    - exercise/106_files.zig, or
+//    - create a file {project_root}/output/zigling.txt
+//      with content `It's zigling time!`(18 byte total)
+//
+// Now there no point in writing to a file if we don't read from it am I right?
+// let's write a program to read the content of the file that we just created.
+//
+// I am assuming that you've created the appropriate files for this to work.
+//
+// Alright, bud, lean in close here's the game plan.
+//    - First, we open the {project_root}/output/ directory
+//    - Secondly, we open file `zigling.txt` in that directory
+//    - then, we initalize an array of characters with all letter 'A', and print it
+//    - After that, we read the content of the file to the array
+//    - Finally, we print out the read content
+
+const std = @import("std");
+
+pub fn main() !void {
+    // Get the current working directory
+    const cwd = std.fs.cwd();
+
+    // try to open ./output assuming you did your 106_files exercise
+    var output_dir = try cwd.openDir("output", .{});
+    defer output_dir.close();
+
+    // try to open the file
+    const file = try output_dir.openFile("zigling.txt", .{});
+    defer file.close();
+
+    // initalize an array of u8 with all letter 'A'.
+    // we need to pick the size of the array, 64 seems like a good number.
+    // fix the initalization below
+    var content = ['A']*64;
+    // this should print out : `AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA`
+    std.debug.print("{s}\n", .{content});
+
+    // okay, seems like a threat of violence is not the answer in this case
+    // can you go here to find a way to read the content ?
+    // https://ziglang.org/documentation/master/std/#std.fs.File
+    // hint: you might find two answers that are both vaild in this case
+    const bytes_read = zig_read_the_file_or_i_will_fight_you(&content);
+
+    // Woah, too screamy, I know you're excited for zigling time but tone it down a bit
+    // Can you print only what we read from the file ?
+    std.debug.print("Successfully Read {d} bytes: {s}\n", .{
+        bytes_read,
+        content, // change this line only
+    });
+}

patches/patches/025_errors5.patch

@@ -1,11 +1,11 @@
---- exercises/025_errors5.zig	2023-10-03 22:15:22.122241138 +0200
-+++ answers/025_errors5.zig	2023-10-05 20:04:06.952764946 +0200
+--- exercises/025_errors5.zig	2023-11-21 14:22:48.159250165 +0100
++++ answers/025_errors5.zig	2023-11-21 14:25:01.338277886 +0100
 @@ -26,7 +26,7 @@
      // This function needs to return any error which might come back from detect().
      // Please use a "try" statement rather than a "catch".
      //
--    var x = detect(n);
-+    var x = try detect(n);
+-    const x = detect(n);
++    const x = try detect(n);
  
      return x + 5;
  }

patches/patches/046_optionals2.patch

@@ -1,5 +1,5 @@
---- exercises/046_optionals2.zig	2023-10-03 22:15:22.122241138 +0200
-+++ answers/046_optionals2.zig	2023-10-05 20:04:07.049433424 +0200
+--- exercises/046_optionals2.zig	2024-05-10 23:11:25.796632478 +0200
++++ answers/046_optionals2.zig	2024-05-10 23:10:16.115335668 +0200
 @@ -21,7 +21,7 @@
  
  const Elephant = struct {
@@ -9,12 +9,11 @@
      visited: bool = false,
  };
  
-@@ -51,7 +51,7 @@
+@@ -51,6 +51,6 @@
          // We should stop once we encounter a tail that
          // does NOT point to another element. What can
          // we put here to make that happen?
--        if (e.tail == null) ???;
-+        if (e.tail == null) break;
- 
-         e = e.tail.?;
+-        e = e.tail ???
++        e = e.tail orelse break;
      }
+ }

patches/patches/051_values.patch

@@ -1,5 +1,5 @@
---- exercises/051_values.zig	2023-10-03 22:15:22.122241138 +0200
-+++ answers/051_values.zig	2023-10-05 20:04:07.072767194 +0200
+--- exercises/051_values.zig	2024-03-14 23:25:42.695020607 +0100
++++ answers/051_values.zig	2024-03-14 23:28:34.525109174 +0100
 @@ -87,7 +87,7 @@
      // Let's assign the std.debug.print function to a const named
      // "print" so that we can use this new name later!
@@ -9,7 +9,7 @@
  
      // Now let's look at assigning and pointing to values in Zig.
      //
-@@ -152,13 +152,13 @@
+@@ -163,13 +163,13 @@
      print("XP before:{}, ", .{glorp.experience});
  
      // Fix 1 of 2 goes here:

patches/patches/060_floats.patch

@@ -1,11 +1,11 @@
---- exercises/060_floats.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/060_floats.zig	2023-10-05 20:04:07.112767942 +0200
+--- exercises/060_floats.zig	2023-11-06 19:45:03.609687304 +0100
++++ answers/060_floats.zig	2023-11-06 19:44:49.249419994 +0100
 @@ -43,7 +43,7 @@
      //
-     // We'll convert this weight from tons to kilograms at a
-     // conversion of 907.18kg to the ton.
--    const shuttle_weight: f16 = 907.18 * 2200;
-+    const shuttle_weight: f32 = 907.18 * 2200.0;
+     // We'll convert this weight from pound to kilograms at a
+     // conversion of 0.453592kg to the pound.
+-    const shuttle_weight: f16 = 0.453592 * 4480e6;
++    const shuttle_weight: f32 = 0.453592 * 4.480e6;
  
      // By default, float values are formatted in scientific
      // notation. Try experimenting with '{d}' and '{d:.3}' to see

patches/patches/067_comptime2.patch

@@ -1,5 +1,5 @@
---- exercises/067_comptime2.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/067_comptime2.zig	2023-10-05 20:04:07.146101899 +0200
+--- exercises/067_comptime2.zig	2023-11-21 14:36:12.080295365 +0100
++++ answers/067_comptime2.zig	2023-11-21 15:11:50.814098876 +0100
 @@ -35,7 +35,7 @@
      // In this contrived example, we've decided to allocate some
      // arrays using a variable count! But something's missing...
@@ -8,4 +8,4 @@
 +    comptime var count = 0;
  
      count += 1;
-     var a1: [count]u8 = .{'A'} ** count;
+     const a1: [count]u8 = .{'A'} ** count;

patches/patches/075_quiz8.patch

@@ -1,5 +1,5 @@
---- exercises/075_quiz8.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/075_quiz8.zig	2023-10-05 20:04:07.182769252 +0200
+--- exercises/075_quiz8.zig	2023-11-21 14:48:15.440702720 +0100
++++ answers/075_quiz8.zig	2023-11-21 14:50:23.453311616 +0100
 @@ -49,7 +49,11 @@
  //
  // Please fill in the body of this function!

patches/patches/080_anonymous_structs.patch

@@ -1,18 +1,18 @@
---- exercises/080_anonymous_structs.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/080_anonymous_structs.zig	2023-10-05 20:04:07.202769626 +0200
+--- exercises/080_anonymous_structs.zig	2023-11-21 14:52:54.312749682 +0100
++++ answers/080_anonymous_structs.zig	2023-11-21 14:52:43.909225238 +0100
 @@ -48,13 +48,13 @@
      // * circle1 should hold i32 integers
      // * circle2 should hold f32 floats
      //
--    var circle1 = ??? {
-+    var circle1 = Circle(i32){
+-    const circle1 = ??? {
++    const circle1 = Circle(i32){
          .center_x = 25,
          .center_y = 70,
          .radius = 15,
      };
  
--    var circle2 = ??? {
-+    var circle2 = Circle(f32){
+-    const circle2 = ??? {
++    const circle2 = Circle(f32){
          .center_x = 25.234,
          .center_y = 70.999,
          .radius = 15.714,

patches/patches/094_c_math.patch

@@ -1,6 +1,6 @@
---- exercises/094_c_math.zig	2023-10-22 14:00:02.909379696 +0200
-+++ answers/094_c_math.zig	2023-10-22 14:02:46.709025235 +0200
-@@ -19,7 +19,7 @@
+--- exercises/094_c_math.zig	2024-02-28 12:50:35.789939935 +0100
++++ answers/094_c_math.zig	2024-02-28 12:53:57.910309471 +0100
+@@ -26,7 +26,7 @@
  
  const c = @cImport({
      // What do we need here?

patches/patches/096_memory_allocation.patch

@@ -1,11 +1,11 @@
---- exercises/096_memory_allocation.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/096_memory_allocation.zig	2023-10-05 20:04:07.276104333 +0200
+--- exercises/096_memory_allocation.zig	2023-11-21 14:55:33.805678390 +0100
++++ answers/096_memory_allocation.zig	2023-11-21 14:56:00.236163484 +0100
 @@ -64,7 +64,7 @@
      const allocator = arena.allocator();
  
      // allocate memory for this array
--    var avg: []f64 = ???;
-+    var avg: []f64 = try allocator.alloc(f64, arr.len);
+-    const avg: []f64 = ???;
++    const avg: []f64 = try allocator.alloc(f64, arr.len);
  
      runningAverage(arr, avg);
      std.debug.print("Running Average: ", .{});

patches/patches/104_threading.patch

@@ -0,0 +1,17 @@
+--- exercises/104_threading.zig	2024-04-10 19:12:29.878856370 +0200
++++ answers/104_threading.zig	2024-04-10 19:11:22.304265713 +0200
+@@ -97,12 +97,12 @@
+         defer handle.join();
+ 
+         // Second thread
+-        const handle2 = try std.Thread.spawn(.{}, thread_function, .{-4}); // that can't be right?
++        const handle2 = try std.Thread.spawn(.{}, thread_function, .{2});
+         defer handle2.join();
+ 
+         // Third thread
+         const handle3 = try std.Thread.spawn(.{}, thread_function, .{3});
+-        defer ??? // <-- something is missing
++        defer handle3.join();
+ 
+         // After the threads have been started,
+         // they run in parallel and we can still do some work in between.

patches/patches/105_threading2.patch

@@ -0,0 +1,13 @@
+--- exercises/105_threading2.zig	2024-03-23 16:35:14.754540802 +0100
++++ answers/105_threading2.zig	2024-03-23 16:38:00.577539733 +0100
+@@ -81,8 +81,8 @@
+         defer handle1.join();
+ 
+         // Second thread to calculate the minus numbers.
+-        ???
+-        
++        const handle2 = try std.Thread.spawn(.{}, thread_pi, .{ &pi_minus, 3, count });
++        defer handle2.join();
+     }
+     // Here we add up the results.
+     std.debug.print("PI ≈ {d:.8}\n", .{4 + pi_plus - pi_minus});

patches/patches/106_files.patch

@@ -0,0 +1,29 @@
+--- exercises/106_files.zig	2024-05-05 00:48:25.808548611 +0200
++++ answers/106_files.zig	2024-05-05 01:00:40.742969819 +0200
+@@ -35,7 +35,7 @@
+         // by doing nothing
+         //
+         // we want to catch error.PathAlreadyExists and do nothing
+-        ??? => {},
++        error.PathAlreadyExists => {},
+         // if is any other unexpected error we just propagate it through
+         else => return e,
+     };
+@@ -44,7 +44,7 @@
+     // wait a minute
+     // opening a directory might fail!
+     // what should we do here?
+-    var output_dir: std.fs.Dir = cwd.openDir("output", .{});
++    var output_dir: std.fs.Dir = try cwd.openDir("output", .{});
+     defer output_dir.close();
+ 
+     // we try to open the file `zigling.txt`,
+@@ -55,7 +55,7 @@
+     // but here we are not yet done writing to the file
+     // if only there were a keyword in zig that
+     // allows you "defer" code execute to the end of scope...
+-    file.close();
++    defer file.close();
+ 
+     // !you are not allowed to switch these two lines above the file closing line!
+     const byte_written = try file.write("It's zigling time!");

patches/patches/107_files2.patch

@@ -0,0 +1,26 @@
+--- exercises/107_files2.zig	2024-05-05 00:48:25.808548611 +0200
++++ answers/107_files2.zig	2024-05-05 01:14:03.866062288 +0200
+@@ -33,7 +33,7 @@
+     // initalize an array of u8 with all letter 'A'.
+     // we need to pick the size of the array, 64 seems like a good number.
+     // fix the initalization below
+-    var content = ['A']*64;
++    var content = [_]u8{'A'} ** 64;
+     // this should print out : `AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA`
+     std.debug.print("{s}\n", .{content});
+ 
+@@ -41,12 +41,12 @@
+     // can you go here to find a way to read the content ?
+     // https://ziglang.org/documentation/master/std/#std.fs.File
+     // hint: you might find two answers that are both vaild in this case
+-    const bytes_read = zig_read_the_file_or_i_will_fight_you(&content);
++    const bytes_read = try file.read(&content);
+ 
+     // Woah, too screamy, I know you're excited for zigling time but tone it down a bit
+     // Can you print only what we read from the file ?
+     std.debug.print("Successfully Read {d} bytes: {s}\n", .{
+         bytes_read,
+-        content, // change this line only
++        content[0..bytes_read], // change this line only
+     });
+ }

test/tests.zig

@@ -8,8 +8,8 @@ const mem = std.mem;
 
 const Allocator = std.mem.Allocator;
 const Child = std.process.Child;
-const Build = std.build;
-const FileSource = std.Build.FileSource;
+const Build = std.Build;
+const LazyPath = std.Build.LazyPath;
 const Reader = fs.File.Reader;
 const RunStep = std.Build.RunStep;
 const Step = Build.Step;
@@ -33,7 +33,7 @@ pub fn addCliTests(b: *std.Build, exercises: []const Exercise) *Step {
             const n = ex.number();
 
             const cmd = b.addSystemCommand(&.{
-                b.zig_exe,
+                b.graph.zig_exe,
                 "build",
                 "-Dhealed",
                 b.fmt("-Dhealed-path={s}", .{tmp_path}),
@@ -69,7 +69,7 @@ pub fn addCliTests(b: *std.Build, exercises: []const Exercise) *Step {
 
         // TODO: when an exercise is modified, the cache is not invalidated.
         const cmd = b.addSystemCommand(&.{
-            b.zig_exe,
+            b.graph.zig_exe,
             "build",
             "-Dhealed",
             b.fmt("-Dhealed-path={s}", .{tmp_path}),
@@ -99,7 +99,7 @@ pub fn addCliTests(b: *std.Build, exercises: []const Exercise) *Step {
                 const n = ex.number();
 
                 const cmd = b.addSystemCommand(&.{
-                    b.zig_exe,
+                    b.graph.zig_exe,
                     "build",
                     b.fmt("-Dn={}", .{n}),
                 });
@@ -132,9 +132,9 @@ fn createCase(b: *Build, name: []const u8) *Step {
 const CheckNamedStep = struct {
     step: Step,
     exercise: Exercise,
-    stderr: FileSource,
+    stderr: LazyPath,
 
-    pub fn create(owner: *Build, exercise: Exercise, stderr: FileSource) *CheckNamedStep {
+    pub fn create(owner: *Build, exercise: Exercise, stderr: LazyPath) *CheckNamedStep {
         const self = owner.allocator.create(CheckNamedStep) catch @panic("OOM");
         self.* = .{
             .step = Step.init(.{
@@ -152,7 +152,7 @@ const CheckNamedStep = struct {
 
     fn make(step: *Step, _: *std.Progress.Node) !void {
         const b = step.owner;
-        const self = @fieldParentPtr(CheckNamedStep, "step", step);
+        const self: *CheckNamedStep = @alignCast(@fieldParentPtr("step", step));
         const ex = self.exercise;
 
         const stderr_file = try fs.cwd().openFile(
@@ -180,12 +180,12 @@ const CheckNamedStep = struct {
 const CheckStep = struct {
     step: Step,
     exercises: []const Exercise,
-    stderr: FileSource,
+    stderr: LazyPath,
 
     pub fn create(
         owner: *Build,
         exercises: []const Exercise,
-        stderr: FileSource,
+        stderr: LazyPath,
     ) *CheckStep {
         const self = owner.allocator.create(CheckStep) catch @panic("OOM");
         self.* = .{
@@ -204,7 +204,7 @@ const CheckStep = struct {
 
     fn make(step: *Step, _: *std.Progress.Node) !void {
         const b = step.owner;
-        const self = @fieldParentPtr(CheckStep, "step", step);
+        const self: *CheckStep = @alignCast(@fieldParentPtr("step", step));
         const exercises = self.exercises;
 
         const stderr_file = try fs.cwd().openFile(
@@ -327,7 +327,7 @@ const FailStep = struct {
 
     fn make(step: *Step, _: *std.Progress.Node) !void {
         const b = step.owner;
-        const self = @fieldParentPtr(FailStep, "step", step);
+        const self: *FailStep = @alignCast(@fieldParentPtr("step", step));
 
         try step.result_error_msgs.append(b.allocator, self.error_msg);
         return error.MakeFailed;
@@ -370,7 +370,7 @@ const HealStep = struct {
 
     fn make(step: *Step, _: *std.Progress.Node) !void {
         const b = step.owner;
-        const self = @fieldParentPtr(HealStep, "step", step);
+        const self: *HealStep = @alignCast(@fieldParentPtr("step", step));
 
         return heal(b.allocator, self.exercises, self.work_path);
     }