Mouse Pointer Restricted in Circle

#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, "D:\\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;
}