5-zombies.cpp

// For each alive zombie..
for (int i = 0; i < ZOMBIE_COUNT; i++) {
    if (zombies[i].alive) {

        // Out of screen -> dead
        if (zombies[i].y > SCREEN_HEIGHT) {
            zombies[i].alive = false;
        }

        // Apply gravity
        zombies[i].vY += world.gravity;
        zombies[i].y += zombies[i].vY;

        // Motion
        zombies[i].x += zombies[i].vX;

        // If zombie has been hit, skip (he will fall down)
        if (zombies[i].state == "state_hit") {
            continue;
        }

        // Deal with platform collision
        if (platformCollision(zombies[i].x, zombies[i].y, zombies[i].w, zombies[i].h)) {
            zombies[i].y = platform.y - zombies[i].h; 
            zombies[i].vY = 0;

            if (zombies[i].state == "state_fall") {
                zombies[i].state = "state_walk";
            }
        } else {
            zombies[i].vX = 0;
            zombies[i].state = "state_fall";
        }

        // If zombie is walking..
        if (zombies[i].state == "state_walk") {

            // Set velocity
            zombies[i].vX = zombieSpeed * zombies[i].dir;

            // Attack survivor if colliding
            if (survivor.state != "state_dead" && collision(zombies[i].x, survivor.x, zombies[i].y, survivor.y, zombies[i].w, survivor.w, zombies[i].h, survivor.h)) {
                
                // Set correct animation frames
                zombies[i].frameX = 0;
                zombies[i].frameY = 2;
              
                // Stop it
                zombies[i].vX = 0;
              
                // Set "attack" flag to false (it will be set once the attack has been carried through)
                zombies[i].attack = false;
              
                // Since we're about to start the attack animation, set this flag to false
                zombies[i].animCompleted = false;
                
                // Change state
                zombies[i].state = "state_attack";
            }
        }
        
        // If the zombie is attacking..
        if (zombies[i].state == "state_attack") {

            // Attack survivor if animation is at the last frame (if survivor is jumping, he's able to avoid the attack)
            if (zombies[i].frameX / zombieAnimSpeed == 3 && !zombies[i].attack && survivor.state != "state_jump") {
                zombies[i].attack = true;
                survivor.frameX = 0;
                survivor.frameY = 4;
                survivor.vX = survivor.vY = 0;
                survivor.animCompleted = false;
                survivor.state = "state_dead";
            }
            
            // Get back to the walk state once the job has been done
            if (zombies[i].animCompleted) {
                zombies[i].frameX = 0;
                zombies[i].frameY = 0;
                zombies[i].state = "state_walk";
            }

        }
    }
}