Woah, %= is an operator! Use it instead of x = x % y.
@@ -58,7 +58,7 @@ impl GameState for State {
);
self.width += 1;
- self.width = self.width % 200;
+ self.width %= 200;
ctx.set_char_size(self.width, 45);
if let Some(key) = ctx.key {
if key == VirtualKeyCode::W {
