Restarting the game
We already determine the size of the arena and the number of zombies by the value of the wave
variable. We must also reset the ammo and gun-related variables, as well as setting wave
and score
to zero at the start of each new game. Find the following code in the event-handling section of the game loop and add the following highlighted code:
// Start a new game while in GAME_OVER state else if (event.key.code == Keyboard::Return &&     state == State::GAME_OVER) {     state = State::LEVELING_UP;     wave = 0;     score = 0;     // Prepare the gun and ammo for next game     currentBullet = 0;     bulletsSpare = 24;     bulletsInClip = 6;     clipSize = 6;     fireRate = 1;     // Reset the player's stats     player...