drawing a rectangle!

[3pid]

Hi!
I`m trying to draw a rectangle in c++ but it doesnt run!
it compiles successfully! but when i run it ,it doesnt show anything on the screen
plz guys! what should i do?
this is my code:

void box(int startx, int starty, int endx, int endy, int color)
   {
       line(startx , starty , endx , starty , color) ;
       line(startx , starty , startx , endy , color) ;
       line(startx , endy , endx , endy , color) ;
       line(endx , starty , endx , endy , color) ;
   }
void line(int startx, int starty, int endx, int endy, int color)
    {
       register int t , distance ;
       int xerr = 0 , yerr = 0 , deltax , deltay ;
       int incx , incy ;
       deltax = endx - startx ;
       deltay = endy - starty ;
       if(deltax > 0)
	  incx = 1 ;
       else if(deltax == 0)
	  incx = 0 ;
       else
	  incx =- 1 ;
       if(deltay > 0)
	  incy = 1 ;
       else if(deltay == 0)
	  incy = 0 ;
       else
	  incy =- 1 ;
       deltax = abs(deltax) ;
       deltay = abs(deltay) ;
       if(deltax > deltay)
	    distance = deltax ;
       else
	    distance = deltay ;
       for(t = 0 ; t < distance + 1 ; t++)  {
	  mempoint(startx , starty , color) ;
	  xerr += deltax ;
	  yerr += deltay ;
	  if(xerr > distance) {
	     xerr -= distance ;
	     startx+=incx ;
	  }
	  if(yerr > distance) {
	      yerr -= distance ;
	      starty+=incy ;
	  }
       }
 }