Sierpinski Carpet

#include <graphics.h>
#include <algorithm>

void square(int xc, int yc, int l)
{
    int x1=xc-l/2,y1=yc-l/2;
    int x2=xc+l/2,y2=yc-l/2;
    int x3=xc+l/2,y3=yc+l/2;
    int x4=xc-l/2,y4=yc+l/2;
    line(x1,y1,x2,y2);
    line(x2,y2,x3,y3);
    line(x3,y3,x4,y4);
    line(x4,y4,x1,y1);
}

void Sierpinski(int xc, int yc, int l)
{
    square(xc-l,yc-l,l/3);
    square(xc,yc-l,l/3);
    square(xc+l,yc-l,l/3);
    square(xc+l,yc,l/3);
    square(xc+l,yc+l,l/3);
    square(xc,yc+l,l/3);
    square(xc-l,yc+l,l/3);
    square(xc-l,yc,l/3);
    if (l>9)
    {
        Sierpinski(xc-l,yc-l,l/3);
        Sierpinski(xc,yc-l,l/3);
        Sierpinski(xc+l,yc-l,l/3);
        Sierpinski(xc+l,yc,l/3);
        Sierpinski(xc+l,yc+l,l/3);
        Sierpinski(xc,yc+l,l/3);
        Sierpinski(xc-l,yc+l,l/3);
        Sierpinski(xc-l,yc,l/3);
    }
}

int main()
{
    initwindow(1900, 1000);

    const int xc=getmaxx()/2,yc=getmaxy()/2,l=std::min(getmaxx(),getmaxy())-50;

    square(xc,yc,l);
    square(xc,yc,l/3);
    Sierpinski(xc,yc,l/3);

    getch();
    cleardevice();
    closegraph();

    return 0;
}