Merge upstream with solutions

fix warning

README.md

@@ -1,2 +1,2 @@
 # Ziglings
-# ⚠️ (My solutions, not the [original exercises](https://codeberg.org/ziglings/exercises))
+# ⚠️ My solutions, not the [original exercises](https://codeberg.org/ziglings/exercises)

build.zig

@@ -15,7 +15,7 @@ const print = std.debug.print;
 //     1) Getting Started
 //     2) Version Changes
 comptime {
-    const required_zig = "0.12.0-dev.2618";
+    const required_zig = "0.12.0-dev.3397";
     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];
 
@@ -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.
@@ -939,7 +939,7 @@ 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 +1103,24 @@ 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 = "999_the_end.zig",
         .output =

exercises/047_methods.zig

@@ -88,7 +88,7 @@ pub fn main() void {
         for (&aliens) |*alien| {
 
             // *** Zap the alien with the heat ray here! ***
-            ???.zap(???);
+            heat_ray.zap(alien);
 
             // If the alien's health is still above 0, it's still alive.
             if (alien.health > 0) aliens_alive += 1;

exercises/048_methods2.zig

@@ -54,7 +54,7 @@ fn visitElephants(first_elephant: *Elephant) void {
 
         // This gets the next elephant or stops:
         // which method do we want here?
-        e = if (e.hasTail()) e.??? else break;
+        e = if (e.hasTail()) e.getTail() else break;
     }
 }
 

exercises/049_quiz6.zig

@@ -27,7 +27,13 @@ const Elephant = struct {
     // Your Elephant trunk methods go here!
     // ---------------------------------------------------
 
-    ???
+    pub fn getTrunk(self: *Elephant) *Elephant {
+        return self.trunk.?;
+    }
+
+    pub fn hasTrunk(self: *Elephant) bool {
+        return (self.trunk != null);
+    }
 
     // ---------------------------------------------------
 

exercises/050_no_value.zig

@@ -65,10 +65,10 @@ const std = @import("std");
 const Err = error{Cthulhu};
 
 pub fn main() void {
-    var first_line1: *const [16]u8 = ???;
+    var first_line1: *const [16]u8 = undefined;
     first_line1 = "That is not dead";
 
-    var first_line2: Err!*const [21]u8 = ???;
+    var first_line2: Err!*const [21]u8 = undefined;
     first_line2 = "which can eternal lie";
 
     // Note we need the "{!s}" format for the error union string.
@@ -77,8 +77,8 @@ pub fn main() void {
     printSecondLine();
 }
 
-fn printSecondLine() ??? {
-    var second_line2: ?*const [18]u8 = ???;
+fn printSecondLine() void {
+    var second_line2: ?*const [18]u8 = null;
     second_line2 = "even death may die";
 
     std.debug.print("And with strange aeons {s}.\n", .{second_line2.?});

exercises/051_values.zig

@@ -87,7 +87,7 @@ pub fn main() void {
     // Let's assign the std.debug.print function to a const named
     // "print" so that we can use this new name later!
 
-    const print = ???;
+    const print = std.debug.print;
 
     // Now let's look at assigning and pointing to values in 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
@@ -152,13 +163,13 @@ pub fn main() void {
     print("XP before:{}, ", .{glorp.experience});
 
     // Fix 1 of 2 goes here:
-    levelUp(glorp, reward_xp);
+    levelUp(&glorp, reward_xp);
 
     print("after:{}.\n", .{glorp.experience});
 }
 
 // Fix 2 of 2 goes here:
-fn levelUp(character_access: Character, xp: u32) void {
+fn levelUp(character_access: *Character, xp: u32) void {
     character_access.experience += xp;
 }
 

exercises/052_slices.zig

@@ -32,8 +32,8 @@ pub fn main() void {
     var cards = [8]u8{ 'A', '4', 'K', '8', '5', '2', 'Q', 'J' };
 
     // Please put the first 4 cards in hand1 and the rest in hand2.
-    const hand1: []u8 = cards[???];
-    const hand2: []u8 = cards[???];
+    const hand1: []u8 = cards[0..4];
+    const hand2: []u8 = cards[4..8];
 
     std.debug.print("Hand1: ", .{});
     printHand(hand1);
@@ -43,7 +43,7 @@ pub fn main() void {
 }
 
 // Please lend this function a hand. A u8 slice hand, that is.
-fn printHand(hand: ???) void {
+fn printHand(hand: []u8) void {
     for (hand) |h| {
         std.debug.print("{u} ", .{h});
     }

exercises/053_slices2.zig

@@ -17,19 +17,19 @@ const std = @import("std");
 pub fn main() void {
     const scrambled = "great base for all your justice are belong to us";
 
-    const base1: []u8 = scrambled[15..23];
-    const base2: []u8 = scrambled[6..10];
-    const base3: []u8 = scrambled[32..];
+    const base1: []const u8 = scrambled[15..23];
+    const base2: []const u8 = scrambled[6..10];
+    const base3: []const u8 = scrambled[32..];
     printPhrase(base1, base2, base3);
 
-    const justice1: []u8 = scrambled[11..14];
-    const justice2: []u8 = scrambled[0..5];
-    const justice3: []u8 = scrambled[24..31];
+    const justice1: []const u8 = scrambled[11..14];
+    const justice2: []const u8 = scrambled[0..5];
+    const justice3: []const u8 = scrambled[24..31];
     printPhrase(justice1, justice2, justice3);
 
     std.debug.print("\n", .{});
 }
 
-fn printPhrase(part1: []u8, part2: []u8, part3: []u8) void {
+fn printPhrase(part1: []const u8, part2: []const u8, part3: []const u8) void {
     std.debug.print("'{s} {s} {s}.' ", .{ part1, part2, part3 });
 }

exercises/054_manypointers.zig

@@ -33,7 +33,7 @@ pub fn main() void {
     // we can CONVERT IT TO A SLICE. (Hint: we do know the length!)
     //
     // Please fix this line so the print statement below can print it:
-    const zen12_string: []const u8 = zen_manyptr;
+    const zen12_string: []const u8 = zen_manyptr[0..21];
 
     // Here's the moment of truth!
     std.debug.print("{s}\n", .{zen12_string});

exercises/055_unions.zig

@@ -59,8 +59,8 @@ pub fn main() void {
     std.debug.print("Insect report! ", .{});
 
     // Oops! We've made a mistake here.
-    printInsect(ant, AntOrBee.c);
-    printInsect(bee, AntOrBee.c);
+    printInsect(ant, AntOrBee.a);
+    printInsect(bee, AntOrBee.b);
 
     std.debug.print("\n", .{});
 }

exercises/056_unions2.zig

@@ -44,14 +44,14 @@ pub fn main() void {
     std.debug.print("Insect report! ", .{});
 
     // Could it really be as simple as just passing the union?
-    printInsect(???);
-    printInsect(???);
+    printInsect(ant);
+    printInsect(bee);
 
     std.debug.print("\n", .{});
 }
 
 fn printInsect(insect: Insect) void {
-    switch (???) {
+    switch (insect) {
         .still_alive => |a| std.debug.print("Ant alive is: {}. ", .{a}),
         .flowers_visited => |f| std.debug.print("Bee visited {} flowers. ", .{f}),
     }

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/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/104_threading.zig

@@ -0,0 +1,129 @@
+//
+// 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 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((1) * std.time.ns_per_s);
+        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.debug.print("thread {d}: {s}\n", .{ num, "started." });
+    std.time.sleep((5 - num % 3) * 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, we
+// 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 diggits. 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 diggits.

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/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/104_threading.patch

@@ -0,0 +1,17 @@
+--- exercises/104_threading.zig	2024-03-05 09:09:04.013974229 +0100
++++ answers/104_threading.zig	2024-03-05 09:12:03.987162883 +0100
+@@ -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});