#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <graphics.h>
#define TOP    8
#define BOTTOM 4
#define LEFT   2
#define RIGHT  1
#define ACC(c1,c2) ((c1 == 0) && (c2 == 0))
#define REJ(c1,c2) ((c1 & c2) != 0)
void swap(int *c1, int *c2) { int t; t=*c1; *c1=*c2; *c2=t; }
int getcode (int x, int y) {
  int code;
  if (y > 479) code=BOTTOM;
  else if (y < 0) code=TOP;
  else code=0;
  if (x > 639) code |= RIGHT;
  else if (x < 0) code |= LEFT;
  return code;
}
void main() {
int    Driver;             /* The Graphics device driver           */
int    Mode;               /* The Graphics mode value              */
struct point { int x,y; } p1,p2,p3,p4;
int c2,c1;
float x,y;

  printf("give me the 1st line point--->"); scanf("%d %d",&p1.x,&p1.y);
  printf("give me the 2nd line point--->"); scanf("%d %d",&p2.x,&p2.y);
  getche(); p3=p1; p4=p2;

  c1=getcode(p1.x,p1.y); c2=getcode(p2.x,p2.y);
  if (REJ(c1,c2)) printf("line cannot draw !!!\n");
  else {
    printf("(%d,%d) --> code=%d\n",p1.x,p1.y,c1);
    printf("(%d,%d) --> code=%d\n",p2.x,p2.y,c2); getche(); x=p1.x; y=p1.y;
    while (!ACC(c1,c2)) {
      if (c1 == 0) {
	swap(&c1,&c2); swap(&p1.x,&p2.x); swap(&p1.y,&p2.y); x=p1.x; y=p1.y;
      }
      else
       if (c1 & TOP) {
	x+=(p2.x-p1.x)*(0.0-p1.y)/(p2.y-p1.y); y=p1.y=0; p1.x=(int) x;
       }
       else
	if (c1 & BOTTOM) {
	 x+=(p2.x-p1.x)*(479.0-p1.y)/(p2.y-p1.y); y=p1.y=479; p1.x=(int) x;
	}
	else
	 if (c1 & LEFT) {
	  y+=(p2.y-p1.y)*(0.0-p1.x)/(p2.x-p1.x); x=p1.x=0; p1.y=(int) y;
	 }
	 else if (c1 & RIGHT) {
	  y+=(p2.y-p1.y)*(639.0-p1.x)/(p2.x-p1.x); x=p1.x=639; p1.y=(int) y;
	 }
      c1=getcode(x,y);
    }/* end while */
  } /* end else */
  printf("original line --> (%d,%d) - (%d,%d)\n",p3.x,p3.y,p4.x,p4.y);
  printf("clipping line --> (%d,%d) - (%d,%d)\n",p1.x,p1.y,p2.x,p2.y);
  getche(); Driver = DETECT; initgraph( &Driver, &Mode, "" );
  line(p3.x,p3.y,p4.x,p4.y); getche(); setcolor(6);
  line(p1.x,p1.y,p2.x,p2.y);
  getche();
  closegraph();                 /* Return the system to text mode       */
}