source code of hand drawing game in c language

Code :
#include<conio.h>
#include<stdio.h>
#include<graphics.h>
#include<dos.h>
union REGS i,o;
main()
{
int gd=DETECT,gm,maxx,maxy,x,y,button,prevx,prevy;
initgraph(&gd,&gm,"c:\tc\bgi");
maxx=getmaxx();
maxy=getmaxy();
rectangle(0,0,maxx,maxy);
setviewport(1,1,maxx-1,maxy-1,1);
if(initmouse()==0)
{
    closegraph();
    restorecrtmode();
    printf("mouse driver not loaded");
    exit(1);
}
restrictmouseptr(1,1,maxx-1,maxy-1);
showmouseptr();

while(!kbhit())
{
getmousepos(&button,&x,&y);
if((button&1)==1)
  {
  hidemouseptr();
  prevx=x;
  prevy=y;

while((button&1)==1)
{
line(prevx,prevy,x,y);
prevx=x;prevy=y;
getmousepos(&button,&x,&y);
}
showmouseptr();
}
}
}

/*initilises mouse*/
initmouse()
{
i.x.ax=0;
int86(0x33,&i,&o);
return(o.x.ax);
}

//display mouse pointer
showmouseptr()
{
i.x.ax=1;
int86(0x33,&i,&o);
}

hidemouseptr()
{
i.x.ax=2;
int86(0x33,&i,&o);
}


//restrict mouse pointer
 restrictmouseptr(int x1,int y1,int x2,int y2)
 {
 i.x.ax=7;
 i.x.cx=x1;
 i.x.dx=x2;
 int86(0x33,&i,&o);

 i.x.ax=8;
 i.x.cx=y1;
 i.x.dx=y2;
 int86(0x33,&i,&o);
 }

 //get mouse coordinates and button status
 getmousepos(int *button,int *x,int *y)
 {
 i.x.ax=3;
 int86(0x33,&i,&o);
 *button=o.x.bx;
 *x=o.x.cx;
 *y=o.x.dx;
  }