## Complete program listing

A complete listing of the program discussed in this lesson is shown in Listing 6 .

Listing 6. Source code for BouncingBallInBox project.

 ```/*Project BouncingBallInBox Displays a ball bouncing around inside of a box. The ball is allowed to move in only four directions: northeast, southeast, southwest, or northwest. When the ball hits a wall of the box, it doesn't bounce in the direction that would normally be expected. Instead it selects one of the four possible directions and bounces in that direction. The ball continues to bounce until the user presses the Esc key, at which point the program terminates. */ #include int width = 220;//width of box int height = 440;//height of box int radius = 5;//radius of ball int x = 110;//initial position of ball int y = 220;//initial position of ball int tempX; int tempY; //Keep track of direction of motion here. //0= northwest 1 = southwest, 2 = northeast, //3 = southeast int dir; void moveBall(){ //Save current location of ball. tempX = x; tempY = y; switch(dir){ case 0: //Direction is northwest. if((x <= radius) || (y <= radius)){ //Ball has collided with either the left wall or // the top wall. //Get a new direction. Note that if the new // direction is the same as the old one, control // will come back to here to get still another // direction the next time the functionis called. dir = rand() % 4; }else{ //No collision, set new location for the ball --x; --y; }//end else break; case 1: //Direction is southwest. if(((x <= radius) || (y >= (height - radius)))){ //get a new direction dir = rand() % 4; }else{ //set new location for the ball --x; ++y; }//end else break; case 2: //Direction is northeast. if(((x >= (width - radius)) || (y <= radius))){ //get a new direction dir = rand() % 4; }else{ //set new location for the ball ++x; --y; }//end else break; case 3: //Direction is southeast if((((x >= (width - radius)) || (y >= (height - radius))))){ //get a new direction dir = rand() % 4; }else{ //set new location for the ball ++x; ++y; }//end else }//end switch //Erase the current image of the ball and draw a new // image at the modified location coordinates. acquire_screen(); circlefill (screen,tempX,tempY,radius,makecol(0,0,0)); circlefill (screen,x,y,radius,makecol( 128, 255, 0)); release_screen(); rest(5);//Delay for five milliseconds }// end moveBall function. int main(){ allegro_init(); install_keyboard(); set_color_depth(32); set_gfx_mode(GFX_AUTODETECT_WINDOWED,width,height,0,0); //Seed the random number generator and set the initial // direction based on a random number. srand (time(NULL)); dir = rand() % 4; //Loop until the user presses the Esc key. while( !key[KEY_ESC]){ moveBall(); }//end while loop return 0; }//end main END_OF_MAIN(); ```