Edge Fill Algorithm to fill a Rectangle

/* PROGRAM FOR POLYGON FILING USING EDGEFILL */
#include<graphics.h>
#include<stdlib.h>
#include<dos.h>
void drawply();
void edgefill(int x1, int x2, int y1, int y2);
main()
{
int gd=DETECT,gm,x,y,x1,x2,y1,y2;

/*  Initialise graphics mode  */
initgraph(&gd,&gm,"C:\\TurboC3\\BGI");

cleardevice();
drawply();

x1=300;
x2=371;
y1=240;
y2=170;

while(x1!=x2&&y1!=y2)
{
   x1++;
   x2--;
   y1--;
   y2++;
edgefill(x1,x2,y1,y2);
}
outtextxy(300,100,"Edge fill");
getch();
closegraph();
return(0);
}

/* FUNCTION TO DRAW A POLYGON */
void drawply()
{
setcolor (RED);
line(300,240,371,240);
line(371,240,371,170);
line(371,170,300,170);
line(300,170,300,240);
}

/* FUNCTION TO FILL POLYGON USING EDGEFILL ALGORITHM */
void edgefill(int x1, int x2, int y1, int y2)
{
  int i;
  for(i=x2;i>=x1;i--)
  {
     putpixel(i,y1,RED);
     delay(5);
  }
  for(i=y1; i>=y2;i--)
  {
    putpixel(x1,i,RED);
    delay(5);
  }
  for(i=x1;i<=x2;i++)
  {
    putpixel(i,y2,RED);
    delay(5);
  }
  for(i=y2; i<=y1;i++)
  {
    putpixel(x2,i,RED);
    delay(5);
  }
}