Circle Drawing Algorithms

#include <stdio.h>
#include <conio.h>
#include <graphics.h>
#include <math.h>

void startgraphics(){
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "");
    cleardevice();
}

void dda(int a, int b, int r){
    int n, count = 0;
    float x = 0, y = r, e;
    for(n=1; ; n++)
        if(pow(2, n-1) <= r && r < pow(2, n)) break;
    e = pow(2, -n);
    do{
        x+=e*y;
        y-=e*x;
        putpixel((int)x+a, (int)y+b, 3);
    }while(count++<r*10); //while(y-sy < e || sx-x > e) gives infinite loop
}

void bres(int a, int b, int r){
    int x = 0, y = r, d = 3-2*r;
    do{
        putpixel(x+a, y+b, 3);
        putpixel(-x+a, y+b, 3);
        putpixel(x+a, -y+b, 3);
        putpixel(-x+a, -y+b, 3);
        putpixel(y+a, x+b, 3);
        putpixel(-y+a, x+b, 3);
        putpixel(y+a, -x+b, 3);
        putpixel(-y+a, -x+b, 3);

        if(d < 0)   d+=4*x+6;
        else {d+= 4*(x-y)+10; y--;}
        x++;
    } while(x < y);
}

void mid(int a, int b, int r){
    int x = 0, y = r;
    float d = 1.25 - r;
    do{
        putpixel(x+a, y+b, 3);
        putpixel(-x+a, y+b, 3);
        putpixel(x+a, -y+b, 3);
        putpixel(-x+a, -y+b, 3);
        putpixel(y+a, x+b, 3);
        putpixel(-y+a, x+b, 3);
        putpixel(y+a, -x+b, 3);
        putpixel(-y+a, -x+b, 3);
        if(d<0){x++; d+=2*x+1;}
        else{x++; y--; d+=2*(x-y)+1;}
    }while(x < y);
}

void main(){
    startgraphics();

    dda(getmaxx()/2, getmaxy()/2, 80);
    bres(getmaxx()/2, getmaxy()/2, 100);
    mid(getmaxx()/2, getmaxy()/2, 150);

    getch();
}