New usize explanation 008, etc.

exercises/008_quiz.zig

@@ -1,7 +1,7 @@
 //
 // Quiz time! Let's see if you can fix this whole program.
 //
-// This is meant to be challenging.
+// You'll have to think about this one a bit.
 //
 // Let the compiler tell you what's wrong.
 //
@@ -13,14 +13,23 @@ pub fn main() void {
     // What is this nonsense? :-)
     const letters = "YZhifg";
 
+    // Note: usize is an unsigned integer type used for...sizes.
+    // The exact size of usize depends on the target CPU
+    // architecture. We could have used a u8 here, but usize is
+    // the idiomatic type to use for array indexing.
+    //
+    // There IS a problem on this line, but 'usize' isn't it.
     const x: usize = 1;
 
-    // This is something you haven't seen before: declaring an array
-    // without putting anything in it. There is no error here:
+    // Note: When you want to declare memory (an array in this
+    // case) without putting anything in it, you can set it to
+    // 'undefined'. There is no problem on this line.
     var lang: [3]u8 = undefined;
 
     // The following lines attempt to put 'Z', 'i', and 'g' into the
-    // 'lang' array we just created.
+    // 'lang' array we just created by indexing the array
+    // 'letters' with the variable 'x'. As you can see above, x=1
+    // to begin with.
     lang[0] = letters[x];
 
     x = 3;

patches/patches/008_quiz.patch

@@ -1,12 +1,16 @@
-16c16
-<     const x: u8 = 1;
+22c22
+<     const x: usize = 1;
 ---
->     var x: u8 = 1;
-27c27
+>     var x: usize = 1;
+26c26
+<     // 'undefined'. There is no problem on this line.
+---
+>     // 'undefined'. There is no error here.
+36c36
 <     lang[???] = letters[x];
 ---
 >     lang[1] = letters[x];
-29,30c29,30
+38,39c38,39
 <     x = ???;
 <     lang[2] = letters[???];
 ---