/*COMPLIED BY SANDESH.PROGRAN FOR BRESAMHEN'S ALGORITHM*/
#include<stdio.h>
#include<graphics.h>
#include<conio.h>
#include<math.h>
int gd=DETECT,gm;
int Xa,Ya,Xb,Yb,dx,dy,x,y,xend,yend;
long int p;
void main()
 {
 detectgraph(&gm,&gd);
 initgraph(&gm,&gd,"C:\\TC\\BGI");
 printf("\nSTART POINT");
 printf("\nENTER THE Xa-COORDINATE->");
 scanf("%d",&Xa);
 printf("\nENTER THE Ya-COORDINATE ->");
 scanf("%d",&Ya);
 printf("\nFOR END POINT");
 printf("\nENTER THE Xb-COORDINATE ->");
 scanf("%d",&Xb);
 printf("\nENTER THE Yb-COORDINATE ->");
 scanf("%d",&Yb);
 dx=Xb-Xa;
 dy=Yb-Ya;
 if(((dy>=0&&dx>0)||(dy<=0&&dx<0))&&(abs(dx)>=abs(dy)))
 gentle_p();
 else
 if(((dy>0&&dx>=0)||(dy<0&&dx<=0))&&(abs(dy)>abs(dx)))
 steep_p();
 else
 if(((dy>0&&dx<0)||(dy<0&&dx>0))&&(abs(dy)<=abs(dx)))
 gentle_n();
 else
 if(((dy>0&&dx<0)||(dy<0&&dx>0))&&(abs(dy)>abs(dx)))
 steep_n();
 getch();
 closegraph();
 }

 gentle_p()
 {                      /*start of func*/
  line(Xa,Ya,Xb,Yb);
  printf("\nGENTLE POSITIVE");
  getch();
  clrscr();
  p=2*abs(dy)-abs(dx);
  if(dx>0)
  {
  x=Xa;
  y=Ya;
  xend=Xb;
  }
  else
  {
  x=Xb;
  y=Yb;
  xend=Xa;
  }
  putpixel(x,y,GREEN);
  while(x<=xend)
  {
  x=x+1;
  if(p<=0)
  p=p+2*abs(dy);
  else
  {
  y=y+1;
  p=p+2*(abs(dy)-abs(dx));
  }
  putpixel(x,y,GREEN);
  }                  /*end ofwhile*/
 return(0);
 }                /*end of func*/
 steep_p()
 {                      /*start of func*/
  line(Xa,Ya,Xb,Yb);
  printf("\nSTEEP POSITIVE");
  getch();
  clrscr();
  p=2*abs(dx)-abs(dy);
  if(dy>0)
  {
  x=Xa;
  y=Ya;
  yend=Yb;
  }
  else
  {
  x=Xb;
  y=Yb;
  yend=Ya;
  }
  putpixel(x,y,BLUE);
  while(y<=yend)
  {
  y=y+1;
  if(p<=0)
  p=p+2*abs(dx);
  else
  {
  x=x+1;
  p=p+2*(abs(dx)-abs(dy));
  }
  putpixel(x,y,BLUE);
  }                  /*end ofwhile*/
 return(0);
 }                /*end of func*/

   gentle_n()
 {                      /*start of func*/
  line(Xa,Ya,Xb,Yb);
  printf("\nGENTLE NEGATIVE");
  getch();
  clrscr();
  if(dx>0)
  {
  x=Xa;
  y=Ya;
  xend=Xb;
  }
  else
  {
  x=Xb;
  y=Yb;
  xend=Xa;
  }
  if(dx<0)
  {
  dx=-dx;
  dy=-dy;
  }
  p=2*dy+dx;
  putpixel(x,y,RED);
  while(x<=xend)
  {
  x=x+1;
  if(p>0)
  p=p+2*dy;
  else
  {
  y=y-1;
  p=p+2*(dy+dx);
  }
  putpixel(x,y,RED);
  }                  /*end ofwhile*/
 return(0);
 }                /*end of func*/

  steep_n()
 {                      /*start of func*/
  line(Xa,Ya,Xb,Yb);
  printf("\nSTEEP NEGATIVE");
  getch();
  clrscr();
  if(dy>0)
  {
  x=Xa;
  y=Ya;
  yend=Yb;
  }
  else
  {
  x=Xb;
  y=Yb;
  yend=Ya;
  }
  if(dy<0)
  {
  dx=-dx;
  dy=-dy;
  }
  p=2*dx+dy;
  putpixel(x,y,CYAN);
  while(y<=yend)
  {
  y=y+1;
  if(p>0)
  p=p+2*dx;
  else
  {
  x=x-1;
  p=p+2*(dx+dy);
  }
  putpixel(x,y,CYAN);
  }                  /*end ofwhile*/
 return(0);
 }                /*end of func*/