Can you draw straight lines? Ok, then just do this, where x and y are the centre of your circle, r is the radius, and draw_line(x1,y1,x2,y2) draws a line from x1,y1 to x2,y2:
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float theta=0;
float dth=0.1;//reduce this to get a better circle.
while(theta<2*M_PI){
draw_line(x+r*cos(theta),y+r*sin(theta),
x+r*cos(theta+dth),y+r*sin(theta+dth));//replace draw_line with whatever your library has
theta += dth;
}
But you should also look for a special circle function.