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.

1 files changed, 26 insertions, 8 deletions

diff --git a/04_arrays.zig b/04_arrays.zig
index a509800..0f4ffe1 100644
--- a/04_arrays.zig
+++ b/04_arrays.zig
@@ -1,31 +1,49 @@
 //
 // Let's learn some array basics. Arrays are declared with:
 //
-//   const foo [size]<type> = [size]<type>{ values };
+//   var foo [3]u32 = [3]u32{ 42, 108, 5423 };
 //
 // When Zig can infer the size of the array, you can use '_' for the
 // size. You can also let Zig infer the type of the value so the
 // declaration is much less verbose.
 //
-//   const foo = [_]<type>{ values };
+//   var foo = [_]u32{ 42, 108, 5423 };
+//
+// Get values of an array using array[index] notation:
+//
+//     const bar = foo[3]; // 5423
+//
+// Set values of an array using array[index] notation:
+//
+//     foo[3] = 16;
+//
+// Get the length of an array using the len property:
+//
+//     const length = foo.len;
 //
 const std = @import("std");
 
 pub fn main() void {
-
+    // (Problem 1)
+    // This "const" is going to cause a problem later - can you see what it is?
+    // How do we fix it?
     const some_primes = [_]u8{ 1, 3, 5, 7, 11, 13, 17, 19 };
 
-    // Individual values can be set with '[]' notation. Let's fix
-    // the first prime (it should be 2!):
+    // Individual values can be set with '[]' notation.
+    // Example: This line changes the first prime to 2 (which is correct):
     some_primes[0] = 2;
 
     // Individual values can also be accessed with '[]' notation.
+    // Example: This line stores the first prime in "first":
     const first = some_primes[0];
 
-    // Looks like we need to complete this expression (like 'first'):
-    const fourth = ???;
+    // (Problem 2)
+    // Looks like we need to complete this expression. Use the example
+    // above to set "fourth" to the fourth element of the some_primes array:
+    const fourth = some_primes[???];
 
-    // Use '.len' to get the length of the array:
+    // (Problem 3)
+    // Use the len property to get the length of the array:
     const length = some_primes.???;
 
     std.debug.print("First: {}, Fourth: {}, Length: {}\n",