#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<math.h>
#include<dos.h>
 
int l = 1;
 
void ddaline(int x1, int y1, int x2, int y2)
{
 
    int s, dx, dy, m;
    float xi, yi, x, y;
 
    dx = x2 - x1;
    dy = y2 - y1;
 
    if (abs(dx) > abs(dy))
 s = abs(dx);
    else
 s = abs(dy);
 
    xi = dx / (float) s;
    yi = dy / (float) s;
 
    x = x1;
    y = y1;
 
    putpixel(x1 + 0.5, y1 + 0.5, 15);
 
    for (m = 0; m < s; m++) {
 x += xi;
 y += yi;
 putpixel(x + 0.5, y + 0.5, 15);
    }
}
 
 
void plotpoints1(int x, int y, int cx, int cy)
{
    putpixel(cx + x, cy + y, 15);
    putpixel(cx - x, cy - y, 15);
    putpixel(cx - y, cy + x, 15);
    putpixel(cx + y, cy - x, 15);
    if (l % 20 == 0) {
 ddaline(cx - x, cy - y, cx + x, cy + y);
 ddaline(cx - y, cy + x, cx + y, cy - x);
    }
    l++;
}
 
void plotpoints2(int x, int y, int cx, int cy)
{
 
    putpixel(cx - x, cy + y, 15);
    putpixel(cx + x, cy - y, 15);
    putpixel(cx + y, cy + x, 15);
    putpixel(cx - y, cy - x, 15);
    if (l % 20 == 0) {
 ddaline(cx + x, cy - y, cx - x, cy + y);
 ddaline(cx - y, cy - x, cx + y, cy + x);
    }
    l++;
}
 
 
void mcircle(int cx, int cy, int r)
{
    int x = 0, y, p;
 
    y = r;
    p = 1 - r;
 
 
    while (x < y) {
 plotpoints1(x, y, cx, cy);
 x++;
 if (p < 0)
     p += 2 * x + 1;
 else {
     y--;
     p += 2 * (x - y) + 1;
 }
    }
 
 
 
    x = y + 1;
    while (abs(x) > 0) {
 plotpoints2(x, y, cx, cy);
 x--;
 if (p >= 0)
     p = p - 2 * x - 1;
 else {
     y++;
     p = p - 2 * (x - y) - 1;
 }
    }
}
 
void main()
{
    int gd = DETECT, gm = DETECT;
    int i = 0;
    initgraph(&gd, &gm, "");
 
    while (!kbhit()) {
 if (i > 640)
     i = -200;
 cleardevice();
 mcircle(100 + (i++), 200, 100);
 delay(90);
 i++;
    }
    getch();
}