#include <stdio.h>
#include <conio.h>
#include <graphics.h>
#include <math.h>
void main()
{
 int gd=DETECT;
 int gm=DETECT;
 int dx,dy,Xa,Ya,Xb,Yb,c,r,p,f,m;
 detectgraph(&gm, &gd);
 initgraph(&gm,&gd,"c:\\tc\\bgi");
 cleardevice();
 printf("\n\n\t\t\t        MAIN MENU\n");
 printf("\t\t\t1.GENTLE POSITIVE SLOPE.\n");
 printf("\t\t\t2.GENTLE NEGATIVE SLOPE.\n");
 printf("\t\t\t3.SHARP  POSITIVE SLOPE.\n");
 printf("\t\t\t4.SHARP  NEGATIVE SLOPE.\n\n");
 printf("\t\t\t   ENTER YOUR CHOICE : ");
 scanf("%d",&m);
 switch(m)
 {
  case 1:
         printf("\n\n\n\n\t\t\tEnter your first X-coordinates: ");
         scanf("%d",&Xa);
         printf("\t\t\tEnter your first Y-coordinates: ");
         scanf("%d",&Ya);
         printf("\t\t\tEnter your second X-coordinates: ");
         scanf("%d",&Xb);
         printf("\t\t\tEnter your second Y-coordinates: ");
         scanf("%d",&Yb);
         dx=Xb-Xa;
         dy=Yb-Ya;
	 p=2*dy-dx;
	 if(Xa>Xb)
         {
           c=Xb;
           r=Yb;
           f=Xa;
         }
         else
         {
          c=Xa;
          r=Ya;
          f=Xb;
         }
         putpixel(c,r,YELLOW);
         do
         {
           c=c+1;
           if(p<0)
            p=p+2*dy;
           else
           {
            r=r+1;
            p=p+2*(dy-dx);
           }
           putpixel(c,r,YELLOW);
         }while(c<f);
	getch();
	line(Xa,Ya,Xb,Yb);
	getch();
	break;

 case 2:
        printf("\n\n\n\n\t\t\tEnter your first X-coordinates: ");
         scanf("%d",&Xa);
         printf("\t\t\tEnter your first Y-coordinates: ");
         scanf("%d",&Ya);
         printf("\t\t\tEnter your second X-coordinates: ");
         scanf("%d",&Xb);
         printf("\t\t\tEnter your second Y-coordinates: ");
         scanf("%d",&Yb);
                 printf("\n\n\n\n\n\t\t\t\t      WAIT!");
         dx=Xb-Xa;
                 dy=Yb-Ya;
         p=2*dy+dx;
         if(Xa<Xb)
         {
           c=Xa;
           r=Ya;
           f=Xb;
         }
         else
         {
          c=Xb;
          r=Yb;
          f=Xa;
         }
         putpixel(c,r,YELLOW);
         do
         {
           c=c+1;
           if(p>0)
            p=p+2*dy;
           else
         {
            r=r-1;
            p=p+2*(dy+dx);
           }
           putpixel(c,r,YELLOW);
         }
         while(c<=f);
         getch();
         line(Xa,Ya,Xb,Yb);
         getch();
	 break;

  case 3:
         printf("\n\n\n\n\t\t\tEnter your first X-coordinates: ");
         scanf("%d",&Xa);
         printf("\t\t\tEnter your first Y-coordinates: ");
         scanf("%d",&Ya);
         printf("\t\t\tEnter your second X-coordinates: ");
         scanf("%d",&Xb);
         printf("\t\t\tEnter your second Y-coordinates: ");
         scanf("%d",&Yb);
         printf("\n\n\n\n\n\t\t\t\t      WAIT!");
         dx=Xb-Xa;
         dy=Yb-Ya;
         p=2*dx-dy;
         if(Ya<Yb)
         {
           c=Xa;
           r=Ya;
           f=Yb;
         }
         else
         {
          c=Xb;
          r=Yb;
          f=Ya;
         }
         putpixel(c,r,YELLOW);
         do
         {
           r=r+1;
           if(p<=0)
            p=p+2*dx;
           else
         {
            c=c+1;
            p=p+2*(dx-dy);
           }
           putpixel(c,r,YELLOW);
         }
         while(r<=f);
         getch();
	 line(Xa,Ya,Xb,Yb);
	 getch();
	 break;

  case 4:
        printf("\n\n\n\n\t\t\tEnter your first X-coordinates: ");
         scanf("%d",&Xa);
         printf("\t\t\tEnter your first Y-coordinates: ");
         scanf("%d",&Ya);
         printf("\t\t\tEnter your second X-coordinates: ");
         scanf("%d",&Xb);
         printf("\t\t\tEnter your second Y-coordinates: ");
         scanf("%d",&Yb);
         printf("\n\n\n\n\n\t\t\t\t      WAIT!");
         dx=fabs(Xb-Xa);
         dy=fabs(Yb-Ya);
         p=dy-2*(dx);
         if(Ya  > Yb)
         {
           c=Xb;
           r=Yb ;
           f=Ya;
         }
         else
         {
          c=Xa;
          r=Ya;
          f=Yb;
         }
         do
         {
           if(p<0)
           {
	    c=c-1;
	    r=r+1;
            p=p-2*(fabs(dx)-fabs(dy));
            }
           else
           {
             r=r+1;
             p=(p-2*fabs(dx));
           }
           putpixel(c,r,YELLOW);
         }
         while(r<=f);
         getch();
         line(Xa,Ya,Xb,Yb);
         getch();
         break;
        
  default:invalid();
	  break;
  }
 }

 blackout()
 {
  int i,j;
  for(i=0;i<640;i++)
  {
   for(j=0;j<480;j++)
    putpixel(j,i,BLACK);
  }
 }

 invalid()
 {
  blackout();
  halfscr();
  printf("\t\t\t\tINVALID INPUT!");
  getch();
  exit();
 }

 halfscr()
 {
  printf("\n\n\n\n\n\n\n\n\n");
 }