3-update.cpp

void update() {

    // Apply gravity
    survivor.vY += world.gravity;
    survivor.y += survivor.vY;

    // Motion
    survivor.x += survivor.vX;

    // If survivor is colliding with the platform..
    if (survivor.y + survivor.h > platform.y &&
        survivor.x + 48 >= platform.x &&
        survivor.x + survivor.w - 48 <= platform.x + platform.w) {
    
        // .. place it on the platform and stop its vertical velocity
        survivor.y = platform.y - survivor.h; 
        survivor.vY = 0;

        // Also, if he was either falling or jumping, get him back to the idle state
        if (survivor.state == "state_fall" || survivor.state == "state_jump") {
            survivor.frameY = 0;
            survivor.state = "state_idle";
        }

    } else if (survivor.state != "state_jump") { // Otherwise, if he's not touching the platform and he's not jumping..
        
        // .. it means that he's falling of course :)
        survivor.state = "state_fall";
    }


    // Input processing
    const Uint8* keys = SDL_GetKeyboardState(NULL);
    
    // If survivor is not doing any unstoppable action (shooting, stabbing or falling)..
    if (survivor.state != "state_shoot" && survivor.state != "state_stab" && survivor.state != "state_fall") {
        
        // If he's jumping
        if (survivor.state == "state_jump") {
            
            // Allow to control his movement while jumping
            if (keys[SDL_SCANCODE_D]) {
                survivor.vX = survivor.speed; // We're tweaking horizontal velocity here..
                survivor.scaleX = 1;
            } else if (keys[SDL_SCANCODE_A]) {
                survivor.vX = -survivor.speed; // .. and here to control flight
                survivor.scaleX = -1;
            } else { // Otherwise, if no keys are currently pressed..
                survivor.vX = 0; // ..stop horizontal velocity (let him fall vertically)
            }
        
        // Otherwise, if he's either walking or standing still..
        } else {
            
            // Detect keyboard keys for jumping, moving or stabbing
            if (keys[SDL_SCANCODE_W]) {
                survivor.vY = -survivor.jumpSpeed; // Notice how we set an initial velocity here!
                survivor.frameY = 3;
                survivor.state = "state_jump";
            } else if (keys[SDL_SCANCODE_J]) {
                survivor.frameX = 0;
                survivor.frameY = 2;
                survivor.vX = 0; // Also walking is now set using velocity
                survivor.animCompleted = false;
                survivor.shot = false;
                survivor.state = "state_shoot";
            } else if (keys[SDL_SCANCODE_K]) {
                survivor.frameX = 0;
                survivor.frameY = 5;
                survivor.vX = 0;
                survivor.animCompleted = false;
                survivor.state = "state_stab";
            } else if (keys[SDL_SCANCODE_D]) {
                survivor.vX = survivor.speed;
                survivor.scaleX = 1;
                survivor.frameY = 1;
                survivor.state = "state_walk";
            } else if (keys[SDL_SCANCODE_A]) {
                survivor.vX = -survivor.speed;
                survivor.scaleX = -1;
                survivor.frameY = 1;
                survivor.state = "state_walk";
            } else {
                survivor.frameY = 0;
                survivor.vX = 0;
                survivor.state = "state_idle";
            }
       }
    }

    // Player states
    
    // If survivor is shooting..
    if (survivor.state == "state_shoot") {

        if (survivor.frameX / survivor.animSpeed == 2 && !survivor.shot) {
            survivor.shot = true;
            shootBullet();
        }

        if (survivor.animCompleted) {
            survivor.frameY = 0;
            survivor.state = "state_idle";
        }
    }

    // If survivor is stabbing (todo: hit zombies)..
    if (survivor.state == "state_stab") {

        if (survivor.animCompleted) {
            survivor.frameY = 0;
            survivor.state = "state_idle";
        }
    }

    // Bullets (nothing new here)
    for (int i = 0; i < BULLET_COUNT; i++) {
        if (bullets[i].alive) {
            bullets[i].x += bulletSpeed * bullets[i].dir;

            if (bullets[i].x + bulletWidth < 0 || bullets[i].x > SCREEN_WIDTH) {
                bullets[i].alive = false;
            }
        }
    }
}