mention builtin ex coming up

exercises/016_for2.zig

@@ -25,6 +25,9 @@ pub fn main() void {
     //
     // See if you can figure out the missing piece:
     for (bits) |bit, ???| {
+        // Note that we convert the usize i to a u32 with
+        // @intCast(), a builtin function just like @import().
+        // We'll learn about these properly in a later exercise.
         var place_value = std.math.pow(u32, 2, @intCast(u32, i));
         value += place_value * bit;
     }

exercises/036_enums2.zig

@@ -5,7 +5,9 @@
 //
 //     const Stuff = enum(u8){ foo = 16 };
 //
-// You can get the integer out with a built-in function:
+// You can get the integer out with a builtin function,
+// @enumToInt(). We'll learn about builtins properly in a later
+// exercise.
 //
 //     var my_stuff: u8 = @enumToInt(Stuff.foo);
 //

exercises/058_quiz7.zig

@@ -419,7 +419,10 @@ pub fn main() void {
 // we need to loop through the items in reverse, skipping nulls, until
 // we reach the destination at the front of the array.
 fn printTrip(trip: []?TripItem) void {
-    var i: u8 = @intCast(u8, trip.len); // convert usize length
+    // We convert the usize length to a u8 with @intCast(), a
+    // builtin function just like @import().  We'll learn about
+    // these properly in a later exercise.
+    var i: u8 = @intCast(u8, trip.len);
 
     while (i > 0) {
         i -= 1;