Listing 6. Negate and display the image. 
  //Cycle through the bitmap negating each pixel.
  for(int row = 0;row < height;row++){
    for(int column = 0;column < width;column++){
      pixel = getpixel(picA,column,row);
      red = getr(pixel);
      green = getg(pixel);
      blue = getb(pixel);
      putpixel(picA,column,row,makecol(
                             255-red,255-green,255-blue));
    }//end loop row
  }//end loop on column

  //Copy the modified bitmap to the onscreen window
  // immediately below the original image.
  blit(picA, screen, 0,0,0,height,width,height);

  //Block and wait until the user presses a key.
  readkey();
  
  //Destroy bitmap to avoid memory leaks.
  destroy_bitmap(picA);

  return 0;//Return 0 to indicate a successful run.
}//end main function
END_OF_MAIN()