allegro question

I have this simulation result from matlab; and my computer is so slow it's painful to make a movie to watch the motion using matlab. So I export the data, and do the animation in allegro instead.

Code:

  while( i < pll.size() && !key[KEY_ESC] ) 
  {
    x = sin(pll[i][1])*double(SCREEN_W)/2.0 + double(SCREEN_W)/2.0-1;
    y = -cos(pll[i][3])*double(SCREEN_H)/2 + double(SCREEN_H)/2.0;
    textprintf_ex(screen,font,0,0,15,-1,
    		  "x = %+5.5lf ; y = %+5.5lf",x,y);
    circle(screen,x,y,3,makecol(255,0,0) );
   
    ++i;
    rest(100);
    textprintf_ex(screen,font,0,0,0,-1,
    		  "x = %+5.5lf ; y = %+5.5lf",x,y);
     circle(screen,x,y,3,0 );
  }

As, you see, that's just a beginner's allegro stuff. It works, but there are a few kinks i want to work out, and maybe you can help me.
1. how do I make the animation go slower? The speed it is going is way too fast to watch.
2. In the below snippet, plotting and then using a different color to erase the previously object seems really wasteful. Is there a way do this better?

Code:

circle(screen,x,y,3,makecol(255,0,0) );
ircle(screen,x,y,3,0);

thanks in advance for any input.

to see each frame individually you could use

Code:

system("PAUSE");

but i have no idea how to set the fps. maybe you should try using <ctime> and having it wait for 1/24 of a second after it displays one frame.