Functions that do pretty things inside windows

//function that returns random floats
float frand() {
    srand(time(NULL));
    return (float)((rand() % 100 + 1) % (rand() % 10 + 1)) / 10;
}

//function that does pretty things inside any window
void illusion(SDL_Window *window) {
    const int screen_width = 500;
    const int screen_height = 500;
    SDL_Renderer *renderer = SDL_CreateRenderer(window, 0, SDL_RENDERER_ACCELERATED);
    SDL_Rect rectangle, rectangle2;
    //default values
    bool quit = false;

    double rect1_x = screen_width / 2, rect1_y = screen_height / 2, rect1_width = 5, rect1_height = 5;
    double rect2_x = screen_width / 2, rect2_y = screen_height / 2, rect2_width = 5, rect2_height = 5;

    while (quit == false)
    {

        float p = frand(), q = frand(), r = frand(), s = frand();
        SDL_Event event;
        while (SDL_PollEvent(&event))
            if (event.type == SDL_QUIT) quit = true;
        rectangle.x = rect1_x, rectangle.y = rect1_y, rectangle.h = rect1_height, rectangle.w = rect1_width;

        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderFillRect(renderer, &rectangle);
        rect1_x -= p;
        rect1_y -= q;
        rect1_width += p*2;
        rect1_height += q*2;
        if (rect1_x < 0 || rect1_y < 0)
        {
            rect1_height = 0;
            rect1_width = 0;
            rect1_x = 0;
            rect1_y = 0;
            if (rect1_x < 250 || rect1_y < 250)
            {
                rectangle2.x = rect2_x;
                rectangle2.y = rect2_y;
                rectangle2.h = rect2_height;
                rectangle2.w = rect2_width;

                SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
                SDL_RenderFillRect(renderer, &rectangle2);
                rect2_x -= r;
                rect2_y -= s;
                rect2_width += 2*r;
                rect2_height += 2*s;
            }
        }
        if (rect2_x < 0 || rect2_y < 0)
        {
            rect2_height = 0;
            rect2_width = 0;
            rect2_x = 250;
            rect2_y = 250;
            rect1_height = 5;
            rect1_width = 5;
            rect1_x = 250;
            rect1_y = 250;
            SDL_Delay(rand() % 10);
        }
        SDL_RenderPresent(renderer);
    }
}

/*
YOU can randomize almost everything! colors! delays!! sprites!! shaders!!! :P
shapes are tough to randomise, I am just a noob in sdl :(
*/