"999 is enough for anybody" triple-zero padding (#18)

When I hit 999 exercises, I will finally have reached the ultimate
state of soteriological release and no more exercises will be needed.
The cycle will be complete. All that will be left is perfect quietude,
freedom, and highest happiness.

1 files changed, 41 insertions, 0 deletions

diff --git a/exercises/041_pointers3.zig b/exercises/041_pointers3.zig
new file mode 100644
index 0000000..9e2bcc6
--- /dev/null
+++ b/exercises/041_pointers3.zig
@@ -0,0 +1,41 @@
+//
+// The tricky part is that the pointer's mutability (var vs const) refers
+// to the ability to change what the pointer POINTS TO, not the ability
+// to change the VALUE at that location!
+//
+//     const locked: u8 = 5;
+//     var unlocked: u8 = 10;
+//
+//     const p1: *const u8 = &locked;
+//     var   p2: *const u8 = &locked;
+//
+// Both p1 and p2 point to constant values which cannot change. However,
+// p2 can be changed to point to something else and p1 cannot!
+//
+//     const p3: *u8 = &unlocked;
+//     var   p4: *u8 = &unlocked;
+//     const p5: *const u8 = &unlocked;
+//     var   p6: *const u8 = &unlocked;
+//
+// Here p3 and p4 can both be used to change the value they point to but
+// p3 cannot point at anything else.
+// What's interesting is that p5 and p6 act like p1 and p2, but point to
+// the value at "unlocked". This is what we mean when we say that we can
+// make a constant reference to any value!
+//
+const std = @import("std");
+
+pub fn main() void {
+    var foo: u8 = 5;
+    var bar: u8 = 10;
+
+    // Please define pointer "p" so that it can point to EITHER foo or
+    // bar AND change the value it points to!
+    ??? p: ??? = undefined;
+
+    p = &foo;
+    p.* += 1;
+    p = &bar;
+    p.* += 1;
+    std.debug.print("foo={}, bar={}\n", .{ foo, bar });
+}