Mid Point Ellipse Algorithm

Computer graphics program in C++

C++

#include <bits/stdc++.h>
#include<graphics.h>
#include<conio.h>
using namespace std;

void elli(int rx, int ry,
                  int xc, int yc)
{
    float dx, dy, d1, d2, x, y;
    x=0;
    y=ry;
    d1=(ry*ry)-(rx*rx*ry)+(0.25 * rx * rx);
    dx=2*ry*ry*x;
    dy=2*rx*rx*y;
    while (dx < dy)
    {
        putpixel(x+xc,y+yc,RED);
        putpixel(-x+xc,y+yc,RED);
        putpixel(x+xc,-y+yc,RED);
        putpixel(-x+xc,-y+yc,RED);
        if (d1 < 0)
        {
            x++;
            dx = dx + (2 * ry * ry);
            d1 = d1 + dx + (ry * ry);
        }
        else
        {
            x++;
            y--;
            dx = dx + (2 * ry * ry);
            dy = dy - (2 * rx * rx);
            d1 = d1 + dx - dy + (ry * ry);
        }
    }
    d2 = ((ry * ry) * ((x + 0.5) * (x + 0.5))) +
         ((rx * rx) * ((y - 1) * (y - 1))) -
          (rx * rx * ry * ry);
    while (y >= 0)
    {
        putpixel(x+xc,y+yc,RED);
        putpixel(-x+xc,y+yc,RED);
        putpixel(x+xc,-y+yc,RED);
        putpixel(-x+xc,-y+yc,RED);
        if (d2 > 0)
        {
            y--;
            dy = dy - (2 * rx * rx);
            d2 = d2 + (rx * rx) - dy;
        }
        else
        {
            y--;
            x++;
            dx = dx + (2 * ry * ry);
            dy = dy - (2 * rx * rx);
            d2 = d2 + dx - dy + (rx * rx);
        }
    }
}

int main()
{
    int xcen,ycen,xr,yr;
    cout<<"Enter x centre:";
    cin>>xcen;
    cout<<"Enter y centre:";
    cin>>ycen;
    cout<<"Enter x radius:";
    cin>>xr;
    cout<<"Enter y radius:";
    cin>>yr;
    int gd=DETECT,gm;
    initgraph(&gd,&gm,"");
    elli(xr,yr,xcen,ycen);
    getch();
    closegraph();
    return 0;
}