changed to require exact start and end values

Resolves: #39

build.zig

@@ -1013,7 +1013,7 @@ const exercises = [_]Exercise{
     },
     .{
         .main_file = "095_for3.zig",
-        .output = "1 2 4 7 8 11 13 14 16 17 19",
+        .output = "3628800",
     },
     .{
         .main_file = "096_memory_allocation.zig",

exercises/095_for3.zig

@@ -45,29 +45,49 @@
 //         std.debug.print("{} ", .{n});
 //     }
 //
-//  Let's try out the new form of 'for' to re-implement that
-//  exercise:
+// We can achieve the same, using a 'for' loop and a range, without
+// having to initialise 'var n':
 //
-const std = @import("std");
-
-pub fn main() void {
-
-    // I want to print every number between 1 and 20 that is NOT
-    // divisible by 3 or 5.
-    for (???) |n| {
-
-        // The '%' symbol is the "modulo" operator and it
-        // returns the remainder after division.
-        if (n % 3 == 0) continue;
-        if (n % 5 == 0) continue;
-        std.debug.print("{} ", .{n});
-    }
-
-    std.debug.print("\n", .{});
-}
+//     for (0..21) |n| {
+//             // The '%' symbol is the "modulo" operator and it
+//             // returns the remainder after division.
+//             if (n % 3 == 0) continue;
+//             if (n % 5 == 0) continue;
+//             std.debug.print("{} ", .{n});
+//         }
 //
 // That's a bit nicer, right?
 //
 // Of course, both 'while' and 'for' have different advantages.
 // Exercises 11, 12, and 14 would NOT be simplified by switching
 // a 'while' for a 'for'.
+//
+//
+// According to wikipedia: In mathematics, the factorial of a
+// non-negative integer n, denoted by n!, is the product of
+// all positive integers less than or equal to n.
+//
+// The factorial can be calculated recursively, but here let's
+// try out the new form of 'for' to calculate 10! :
+//
+const std = @import("std");
+
+const FactorialError = error{ NonPositive };
+
+pub fn main() !void {
+
+    var factorial: u64 = undefined;
+
+    // I want to print 10!
+    for (???) |n| {
+        // 0! is a special case, and by convention equals 1.
+        // we don't handle that case in this exercise
+        if (n < 1) return FactorialError.NonPositive;
+        if (n == 1) {
+            factorial = 1;
+        } else factorial = factorial * n;
+    }
+
+    std.debug.print("{}\n", .{ factorial });
+}
+

patches/patches/095_for3.patch

@@ -1,11 +1,11 @@
---- exercises/095_for3.zig	2023-10-03 22:15:22.125574535 +0200
-+++ answers/095_for3.zig	2023-10-05 20:04:07.272770937 +0200
-@@ -54,7 +54,7 @@
+--- exercises/095_for3.zig	2024-01-14 10:03:37
++++ answers/095_for3.zig	2024-01-14 10:17:06
+@@ -79,7 +79,7 @@
+     var factorial: u64 = undefined;
  
-     // I want to print every number between 1 and 20 that is NOT
-     // divisible by 3 or 5.
+     // I want to print 10!
 -    for (???) |n| {
-+    for (1..21) |n| {
- 
-         // The '%' symbol is the "modulo" operator and it
-         // returns the remainder after division.
++    for (1.11) |n| {
+         // 0! is a special case, and by convention equals 1.
+         // we don't handle that case in this exercise
+         if (n < 1) return FactorialError.NonPositive;