C graphics program to shear a rectangle

#include<graphics.h>
#include<conio.h>
void main()
{
int gd=DETECT,gm,option,xref,yref;
int i,maxx,maxy,x1,y1,x2,y2,x3,y3,x4,y4,gap=50;
float shx=0.0,shy=0.0;
char str[5];
clrscr();
initgraph(&gd,&gm,"..\\bgi");

printf("enter the  endpoints of the top of the rectangle (x1,y1) & (x2,y2):");
 scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
 printf("enter the endpoints of bottom of the rectangle (x3,y3) & (x4,y4)");
 scanf("%d%d%d%d",&x3,&y3,&x4,&y4);
 printf(" Enter the axis to shear\n");
 printf(" 1 - X axis Shear\n");
 printf(" 2 - Y axis shear\n");
 scanf("%d",&option );
 if(option==1)
 {
 printf("enter the value for x-axis shear( can be fraction too):");
 scanf("%f",&shx);
 }
 else
 {
 printf("enter the value for y-axis shear( can be fraction too):");
 scanf("%f",&shy);
 }

clearviewport();
maxx= getmaxx();
maxy=getmaxy();
line(3,maxy-1,maxx-5,maxy-1);
line(5,5,5,maxy-3);

for( i= 0;i<maxx-5;i=i+gap)              // code to display co-ordinates
{
outtextxy(i+3,maxy-7,"|");
itoa(i,str,10);
outtextxy(i,maxy-10,str);
}
for( i= maxy;i>0;i=i-gap)
{
outtextxy(3,i,"-");
itoa(maxy-i,str,10);
outtextxy(9,i,str);

}
 setcolor(50);                // drawing rectangle using endpoints
 line(x1,maxy-y1,x2,maxy-y2);
 line(x3,maxy-y3,x4,maxy-y4);
 line(x1,maxy-y1,x3,maxy-y3);
 line(x2,maxy-y2,x4,maxy-y4);
 outtextxy(10,10,"hit any key to see the shearing effect" );
 getch();
 setcolor(0);    // to hide the rectangle drawn
  line(x1,maxy-y1,x2,maxy-y2);
  line(x3,maxy-y3,x4,maxy-y4);
  line(x1,maxy-y1,x3,maxy-y3);
  line(x2,maxy-y2,x4,maxy-y4);

   setcolor(58);    // to redraw the rectangle
 if(option==1)
  {
  // shearing about x axis so only  points x1 and x2 need to be recomputed
  line(x1+shx*y1,maxy-y1,x2+shx*y2,maxy-y2);
  line(x3,maxy-y3,x4,maxy-y4);
  line(x1+shx*y1,maxy-y1,x3,maxy-y3);
  line(x2+shx*y2,maxy-y2,x4,maxy-y4);

 }
 else
 {
   // shearing about y axis so only  points y2 and y4 need to be recomputed
  line(x1,maxy-y1,x2,maxy-(y2+shy*x2));
  line(x3,maxy-y3,x4,maxy-(y4+shy*x4));
  line(x1,maxy-y1,x3,maxy-y3);
  line(x2,maxy-(y2+shy*x2),x4,maxy-(y4+shy*x4));

 }
 getch();
 closegraph();
}

 
        Original Image             Shearing w.r.t  Y - axis     Shearing w.r.t  X - axis   

Sample Input
    x1 ,y1, x2, y2 : 200 200 300 200
    x3, y3, x4, y4 : 200 100 300 100  
x- shear value: any value even fractional ( eg 0.4)
y- shear value: any value even fractional ( eg 0.5)