Implementation of circle drawing algorithm

1. #include<iostream.h>
2. #include<conio.h>
3. #include<graphics.h>
4. #include<dos.h> 
5. void main()
6. {
7. int gm,gd=DETECT; initgraph(&gd,&gm,"c:\\tc\\bgi"); 
8. int x1,y1;
9. int x=0,y=0,r=0; float d;
10. //textbackground(15);
11. //textcolor(8);
12. //setbkcolor(15);
13. //setcolor(8);
14. cout<<"Enter pixels for centre of a circle (x,y): "; cin>>x1>>y1;
15. cout<<"\nEnter radius of circle: "; cin>>r;
16. x=0;
17. y=r; d=1.25-r;
18. line(0,getmaxy()/2,getmaxx(),getmaxy()/2); line(getmaxx()/2,0,getmaxx()/2,getmaxy()); 
19. do
20. {
21. putpixel(getmaxx()/2+(x1+x),getmaxy()/2-(y1+y),8); 
22. putpixel(getmaxx()/2+(x1-x),getmaxy()/2-(y1+y),8);
23. putpixel(getmaxx()/2+(x1-x),getmaxy()/2-(y1-y),8); 
24. 
    
25. putpixel(getmaxx()/2+(x1+x),getmaxy()/2-(y1-y),8); 
26. 
    
27. putpixel(getmaxx()/2+(x1+y),getmaxy()/2-(y1+x),8); 
28. 
    
29. putpixel(getmaxx()/2+(x1+y),getmaxy()/2-(y1-x),8); 
30. 
    
31. putpixel(getmaxx()/2+(x1-y),getmaxy()/2-(y1-x),8); 
32. 
    
33. putpixel(getmaxx()/2+(x1-y),getmaxy()/2-(y1+x),8); 
34. 
    
35. if(d<0)
36. {
37. x+=1;
38. y=y; 
39. d+=2*x+1;}
40. else
41. {
42.              x+=1; 
43.              y-=1;
44. d+=2*(x-y)+1;
45. }
46. delay(50);
47. }while(x<y);
48. getch();
49. }