Single quotes around character and source in comment

exercises/031_switch2.zig

@@ -29,8 +29,8 @@ pub fn main() void {
             // ...
             25 => 'Y',
             26 => 'Z',
-            // As in the last exercise, please add the "else" clause
+            // As in the last exercise, please add the 'else' clause
-            // and this time, have it return an exclamation mark "!".
+            // and this time, have it return an exclamation mark '!'.
         };
 
         std.debug.print("{c}", .{real_char});