#include <math.h>            /* Needed for sin and cos functions */

void Circle(int xOffset, int yOffset, int radius, unsigned char C)
{
     float xPlot, yPlot;     /* Current pixel being plotted */
     float angle, angleRad;  /* Current angle degrees & radiens */

     for (angle = 0.; angle < 360.; angle += 1) {

          /* Convert degrees to radiens */
          angleRad = angle * (3.141592654 / 180);

          /* Convert polar to rectangular coordinates */
          xPlot = (radius * cos(angleRad)) + xOffset;
          yPlot = (radius * sin(angleRad)) + yOffset;

          /* Check boundaries */
          if (xPlot < 0)
               xPlot = 0;
          else if (xPlot >= ScreenWidth)
               xPlot = ScreenWidth - 1;

          if (yPlot < 0)
               yPlot = 0;
          else if (yPlot >= ScreenHeight)
               yPlot = ScreenHeight - 1;

          /* Plot the pixel on the graphics screen */
          SetPixel((int)xPlot, (int)yPlot, C);
     }
}