Set pixel colors in the off-screen bitmap

Listing 3 uses a pair of nested for loops to:

Listing 3. Set pixel colors in the off-screen bitmap.
  for(int row = 0;row < 255;row++){
    for(int column = 0;column < 255;column++){
      putpixel(buffer,column,row,makecol(column,row,128));
    }//end loop row
  }//end loop on column