Moved exercises to exercises because exercises

exercises/40_pointers2.zig

@@ -0,0 +1,27 @@
+//
+// It's important to note that variable pointers and constant pointers
+// are different types.
+//
+// Given:
+//
+//     var foo: u8 = 5;
+//     const bar: u8 = 5;
+// 
+// Then:
+//
+//     &foo is of type "*u8"
+//     &bar is of type "*const u8"
+//
+// You can always make a constant pointer to a variable, but you cannot
+// make a variable pointer to a constant. This sounds like a logic puzzle,
+// but it just means that once data is declared immutable, you can't
+// coerce it to a mutable type. It's a safety thing (to prevent mistakes).
+//
+const std = @import("std");
+
+pub fn main() void {
+    const a: u8 = 12;
+    const b: *u8 = &a; // fix this!
+
+    std.debug.print("a: {}, b: {}\n", .{a, b.*});
+}