Merge pull request 'fixed formatting error' (#496) from format_error into main

Reviewed-on: https://codeberg.org/ziglings/exercises/pulls/496

exercises/026_hello2.zig

@@ -30,3 +30,11 @@ pub fn main(init: std.process.Init) !void {
     // We just learned of a single statement which can accomplish this.
     stdout.print("Hello world!\n", .{});
 }
+
+// Now you must be thinking "Why would I need to do this instead of good
+// old 'std.debug.print()'?", but here's what you need to understand:
+// 'std.debug.print()' prints its output to stderr, while the stdout_writer
+// approach prints to stdout.
+// A common practice is to pipe output of a command to other commands,
+// and in order for the piping to work, those commands expect their input
+// to come from stdout, not stderr.

exercises/108_threading2.zig

@@ -28,9 +28,9 @@
 // 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
+//          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
@@ -71,27 +71,28 @@
 const std = @import("std");
 
 pub fn main() !void {
-    const count = 1_000_000_000;
+    const count = 500_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 });
+        const handle1 = try std.Thread.spawn(.{}, thread_pi, .{ &pi_plus, 1, 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});
+    std.debug.print("PI ≈ {d:.8} (error = {e:.1})\n", .{ pi_plus - pi_minus, std.math.pi - (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));
+fn thread_pi(pi: *f64, begin: u64, count: u64) !void {
+    for (0..count) |i| {
+        const term = 4 / @as(f64, @floatFromInt(begin + 4 * i));
+        pi.* += term;
     }
 }
 // If you wish, you can increase the number of loop passes, which
@@ -103,8 +104,14 @@ fn thread_pi(pi: *f64, begin: u64, end: u64) !void {
 // is created. Otherwise the debug functions slow down the speed
 // to such an extent that seconds become minutes during execution.
 //
+// You can use the following command to build and run this
+// exercise with the "ReleaseFast" flag:
+//
+//      zig run exercises/108_threading2.zig -O ReleaseFast
+//
 // And you should remove the formatting restriction in "print",
 // otherwise you will not be able to see the additional digits.
 //
-// If count = 10_000_000_000_000 you should see the following:
+// If count = 2_500_000_000_000, you should see the following:
 // 3.141592653589
+// (after waiting on the order of 1000 seconds, or 17 minutes)

patches/patches/026_hello2.patch

@@ -1,9 +1,11 @@
---- exercises/026_hello2.zig	2026-01-09 22:51:45.803358789 +0100
-+++ answers/026_hello2.zig	2026-01-09 22:50:46.016166527 +0100
-@@ -28,5 +28,5 @@
+--- exercises/026_hello2.zig	2026-07-01 16:27:18.674459266 +0200
++++ answers/026_hello2.zig	2026-07-01 16:27:08.579220702 +0200
+@@ -28,7 +28,7 @@
      // 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", .{});
  }
+ 
+ // Now you must be thinking "Why would I need to do this instead of good

patches/patches/036_enums2.patch

@@ -1,5 +1,5 @@
---- exercises/036_enums2.zig	2023-10-03 22:15:22.122241138 +0200
-+++ answers/036_enums2.zig	2023-10-05 20:04:07.002765884 +0200
+--- exercises/036_enums2.zig	2026-07-21 20:48:50.596099259 +0200
++++ answers/036_enums2.zig	2026-07-21 20:50:14.726826859 +0200
 @@ -31,7 +31,7 @@
  const Color = enum(u32) {
      red = 0xff0000,
@@ -18,9 +18,11 @@
          \\</p>
          \\
      , .{
-         @intFromEnum(Color.red),
-         @intFromEnum(Color.green),
+-        @intFromEnum(Color.red),
+-        @intFromEnum(Color.green),
 -        @intFromEnum(???), // Oops! We're missing something!
-+        @intFromEnum(Color.blue), // Oops! We're missing something!
++        @backingInt(Color.red),
++        @backingInt(Color.green),
++        @backingInt(Color.blue), // Oops! We're missing something!
      });
  }

patches/patches/108_threading2.patch

@@ -1,13 +1,12 @@
---- exercises/108_threading2.zig	2026-04-14 06:44:18.848246237 +0200
-+++ answers/108_threading2.zig	2026-04-14 08:15:30.894485037 +0200
-@@ -81,8 +81,8 @@
+--- exercises/108_threading2.zig	2026-06-29 23:25:53
++++ answers/108_threading2.zig	2026-06-29 23:25:25
+@@ -82,7 +82,8 @@
          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});

rivendell/elrond.zig

@@ -359,7 +359,6 @@ fn runExe(ctx: Context, ex: Exercise) !void {
         return err;
     };
 
-    resetLine();
     print("Checking {s}...\n", .{ex.main_file});
 
     return checkOutput(io, arena, ex, result);
@@ -392,7 +391,6 @@ fn runTest(ctx: Context, ex: Exercise) !void {
         return err;
     };
 
-    resetLine();
     print("Checking {s}...\n", .{ex.main_file});
 
     return checkTest(ex, result);
@@ -486,10 +484,6 @@ fn help(ex: Exercise, mode: Mode) void {
     });
 }
 
-fn resetLine() void {
-    if (stderr_term_mode == .escape_codes) print("{s}", .{"\x1b[2K\r"});
-}
-
 // Removes trailing whitespace per line and any trailing LF at the end.
 fn trimLines(arena: std.mem.Allocator, buf: []const u8) ![]const u8 {
     var list = try std.ArrayList(u8).initCapacity(arena, buf.len);
@@ -1173,7 +1167,7 @@ const exercises = [_]Exercise{
     },
     .{
         .main_file = "108_threading2.zig",
-        .output = "PI ≈ 3.14159265",
+        .output = "PI ≈ 3.14159265 (error = 1.0e-9)",
     },
     .{
         .main_file = "109_files.zig",