Explaining undefined 0xAA in 038 (for issue #43)

exercises/038_structs2.zig

@@ -4,7 +4,7 @@
 // them to functions, etc.
 //
 // This exercise demonstrates how we can store structs in an array and
-// how doing so lets us print them all (both) using a loop.
+// how doing so lets us print them using a loop.
 //
 const std = @import("std");
 
@@ -50,3 +50,9 @@ pub fn main() void {
         });
     }
 }
+
+// If you tried running the program without adding Zump as mentioned
+// above, you get what appear to be "garbage" values. In debug mode
+// (which is the default), Zig writes the repeating pattern "10101010"
+// in binary (or 0xAA in hex) to all undefined locations to make them
+// easier to spot when debugging.