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c program to restrict mouse pointer in a circle

This program restricts mouse pointer in a circle i.e you can't move mouse out of a circle. When you try to bring mouse pointer outside the circle, mouse pointer is moved to it's previous location which is inside the circle. Code to restrict mouse in circle is given below :-

C programming code

#include<graphics.h>
#include<conio.h>
#include<dos.h>
#include<stdlib.h>
#include<math.h>
 
union REGS i, o;
 
int initmouse()
{
   i.x.ax = 0;
   int86(0X33, &i, &o);
   return ( o.x.ax );
}
 
void showmouseptr()
{
   i.x.ax = 1;
   int86(0X33, &i, &o);
}
 
void hidemopuseptr()
{
   i.x.ax = 2;
   int86(0X33,&i,&o);
}
 
void getmousepos(int *x, int *y)
{
   i.x.ax = 3;
   int86(0X33, &i, &o);
   *x = o.x.cx;
   *y = o.x.dx;
 
}
 
void movemouseptr(int x, int y)
{
   i.x.ax = 4;
   i.x.cx = x;
   i.x.dx = y;
   int86(0X33, &i, &o);
}
 
main()
{
   int gd = DETECT, gm, midx, midy, radius, x, y, tempx, tempy;
 
   radius = 100;
 
   initgraph(&gd, &gm, "C:\\TC\\BGI");
 
   if(!initmouse())
   {
      closegraph();
      exit(1);
   }
 
   midx = getmaxx()/2;
   midy = getmaxy()/2;
 
   showmouseptr();
   movemouseptr(midx, midy);
   circle(midx, midy, radius);
 
   x = tempx = midx;
   y = tempy = midy;
 
   while(!kbhit())
   {
      getmousepos(&x, &y);
 
      if((pow(x-midx,2)+pow(y-midy,2)-pow(radius,2))>0)
      {
         movemouseptr(tempx, tempy);
         x = tempx;
         y = tempy;
      }
 
      tempx = x;
      tempy = y;
   }
 
   closegraph();
   return 0;
}