BRESENHAM.C

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<math.h>
void main()
{
   int x,a, y, x1, y1, x2, y2, Dx, Dy, twoDx, twoDy, twoDyDx, p, end;
   int gd=DETECT, gm;
   initgraph(&gd,&gm,"C:\\Turboc3\\BGI");
   for(a=1;a<5;a++){
      if(a==1){
	 x1=100;
	 y1=100;
	 x2=150;
	 y2=100;
      }
      if(a==2){
	 x1=100;
	 y1=100;
	 x2=100;
	 y2=150;
      }
      if(a==3){
	 x1=100;
	 y1=150;
	 x2=150;
	 y2=150;
      }
      if(a==4){
	 x1=150;
	 y1=150;
	 x2=150;
	 y2=100;
      }
      if(x1==x2){
	 x=x1;
	 y=y1;
	 while(y!=y2){
	    if((y2-y1)>0)
	       ++y;
	    else
	       --y;
            putpixel(x,y,WHITE);
         }
         if(y1>=y2){
            x=x2;
            y=y2;
            end=y2;
         }
      }
      if(x1<x2){
         x=x1;
         y=y1;
         end=x2;
      }
      else{
         x=x2;
         y=y2;
         end=x1;
      }
      putpixel(x,y,WHITE);
      Dx=abs(x1-x2);
      Dy=abs(y1-y2);
      twoDy=2*Dy;
      twoDyDx=2*(Dy-Dx);
      p=2*Dy-Dx;
      while(x<end){
         if(p<0){
            x++;
            p+=twoDy;
         }
         else{
            x++;
            y++;
            p=twoDyDx;
         }
      putpixel(x,y,WHITE);
      }
   }
   getch();
   closegraph();
}