Consistent instructions and examples

I started off with "hints" that required the poor student to piece
together the information from incomplete bits. A complete example is
like a picture that is worth 1000 words and far clearer.

06_strings.zig

@@ -3,38 +3,46 @@
 // 
 // We've already seen Zig string literals: "Hello world.\n"
 //
-// Like the C language, Zig stores strings as arrays of bytes
-// encoded as UTF-8 characters terminated with a null value.
-// For now, just focus on the fact that strings are arrays of
-// characters!
+// Zig stores strings as arrays of bytes.
+//
+//     const foo = "Hello";
+//
+// Is the same as:
+//
+//     const foo = [_]u8{ 'H', 'e', 'l', 'l', 'o' };
 //
 const std = @import("std");
 
 pub fn main() void {
     const ziggy = "stardust";
 
+    // (Problem 1)
     // Use array square bracket syntax to get the letter 'd' from
     // the string "stardust" above.
     const d: u8 = ziggy[???];
 
+    // (Problem 2)
     // Use the array repeat '**' operator to make "ha ha ha".
     const laugh = "ha " ???;
 
+    // (Problem 3)
     // Use the array concatenation '++' operator to make "Major Tom".
     // (You'll need to add a space as well!)
     const major = "Major";
     const tom = "Tom";
     const major_tom = major ??? tom;
 
+    // That's all the problems. Let's see our results:
     std.debug.print("d={u} {}{}\n",.{d, laugh, major_tom});
-    // Going deeper:
+    //
     // Keen eyes will notice that we've put a 'u' inside the '{}'
     // placeholder in the format string above. This tells the
-    // print() function (which uses std.fmt.format() function) to
-    // print out a UTF-8 character. Otherwise we'd see '100', which
-    // is the decimal number corresponding with the 'd' character
-    // in UTF-8.
+    // print() function to format the values as a UTF-8 character.
+    // If we didn't do this, we'd see '100', which is the decimal
+    // number corresponding with the 'd' character in UTF-8.
+    //
     // While we're on this subject, 'c' (ASCII encoded character)
     // would work in place for 'u' because the first 128 characters
     // of UTF-8 are the same as ASCII!
+    //
 }