#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <graphics.h>
float t[3][3];
void rotate(float th) {
  t[0][0]=t[1][1]=cos(th*3.14159/180); t[2][2]=1;
  t[0][1]=sin(th*3.14159/180); t[1][0]=-t[0][1];
  t[2][0]=t[2][1]=t[1][2]=t[0][2]=0;
}
void tran_point(int oldx,int oldy,int *newx, int *newy) {
  *newx=(int)(t[2][0]+t[0][0]*oldx+t[1][0]*oldy);
  *newy=(int)(t[2][1]+t[0][1]*oldx+t[1][1]*oldy);
}
void main() {
int    GraphDriver;             /* The Graphics device driver           */
int    GraphMode;               /* The Graphics mode value              */
struct viewporttype vp;
float deg;
struct point { int x,y; } p1,p2,p3,p4;

  printf("give me the first point--->"); scanf("%d %d",&p1.x,&p1.y);
  printf("give me the second point--->"); scanf("%d %d",&p2.x,&p2.y);
  printf("give me the rotate angle degree -->"); scanf("%f",&deg);
  getche();

  GraphDriver = DETECT;                 /* Request auto-detection       */
  initgraph( &GraphDriver, &GraphMode, "" );
  setcolor(YELLOW); line(p1.x,p1.y,p2.x,p2.y); getche();
  setcolor(CYAN); rotate(deg);
  p3.x=p2.x-p1.x; p3.y=p2.y-p1.y; /* translate p1 --> (0,0) , so p2 == */
  tran_point(p3.x,p3.y,&p4.x,&p4.y); line(0,0,p3.x,p3.y); getche();
  setcolor(GREEN); line(0,0,p4.x,p4.y); getche();
  line(p1.x,p1.y,p4.x+p1.x,p4.y+p1.y); getche();
  closegraph();                 /* Return the system to text mode       */
}