5-bullets.cpp

// For each alive bullet..
for (int i = 0; i < BULLET_COUNT; i++) {
    if (bullets[i].alive) {
        bullets[i].x += bulletSpeed * bullets[i].dir;

        // Out of screen -> dead
        if (bullets[i].x + bullets[i].w < 0 || bullets[i].x > SCREEN_WIDTH) {
            bullets[i].alive = false;
        }

        // Hit zombie
        hitZombies(&bullets[i]);
    }
}