#include <graphics.h>
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    float x1, y1, x2, y2, x, y, k;
    int gd, gm, i, val, r;
    cout << "Enter the radius of circle ";
    cin >> r;
    initgraph(&gd, &gm, NULL);
    x1 = r * cos(0);
    y1 = r * sin(0);
    x = x1;
    y = y1;
    i = 0;
    do
    {
        val = pow(2, i);
        i++;
    } while (val < r);
    k = 1 / pow(2, i - 1);
    do
    {
        x2 = x1 + y1 * k;
        y2 = y1 - k * x2;
        putpixel(200 + x2, 200 + y2, 15);
        x1 = x2;
        y1 = y2;
    } while ((y1 - y) < k || (x - x1) > k);
    delay(7000);
    return 0;
}

kodingwindow@kw:~$ g++ kw.cpp -lgraph
kodingwindow@kw:~$ ./a.out
Enter the radius of circle 150