bresenham circle drawing algorithm proof code example

Example: bresenham circle drawing algorithm

void    EightWaySymmetricPlot(int xc,int yc,int x,int y)  
   {  
    putpixel(x+xc,y+yc,RED);  
    putpixel(x+xc,-y+yc,YELLOW);  
    putpixel(-x+xc,-y+yc,GREEN);  
    putpixel(-x+xc,y+yc,YELLOW);  
    putpixel(y+xc,x+yc,12);  
    putpixel(y+xc,-x+yc,14);  
    putpixel(-y+xc,-x+yc,15);  
    putpixel(-y+xc,x+yc,6);  
   }  
  
    void BresenhamCircle(int xc,int yc,int r)  
   {  
    int x=0,y=r,d=3-(2*r);  
    EightWaySymmetricPlot(xc,yc,x,y);  
  
    while(x<=y)  
     {  
      if(d<=0)  
             {  
        d=d+(4*x)+6;  
      }  
     else  
      {  
        d=d+(4*x)-(4*y)+10;  
        y=y-1;  
      }  
       x=x+1;  
       EightWaySymmetricPlot(xc,yc,x,y);  
      }  
    }