The two methods used to create circles in opengl

circles.cpp

/*
 * Function that handles the drawing of a circle using the triangle fan
 * method. This will create a filled circle.
 *
 * Params:
 *	x (GLFloat) - the x position of the center point of the circle
 *	y (GLFloat) - the y position of the center point of the circle
 *	radius (GLFloat) - the radius that the painted circle will have
 */
void drawFilledCircle(GLfloat x, GLfloat y, GLfloat radius){
	int i;
	int triangleAmount = 20; //# of triangles used to draw circle
	
	//GLfloat radius = 0.8f; //radius
	GLfloat twicePi = 2.0f * PI;
	
	glBegin(GL_TRIANGLE_FAN);
		glVertex2f(x, y); // center of circle
		for(i = 0; i <= triangleAmount;i++) { 
			glVertex2f(
		            x + (radius * cos(i *  twicePi / triangleAmount)), 
			    y + (radius * sin(i * twicePi / triangleAmount))
			);
		}
	glEnd();
}

/*
 * Function that handles the drawing of a circle using the line loop
 * method. This will create a hollow circle.
 *
 * Params:
 *	x (GLFloat) - the x position of the center point of the circle
 *	y (GLFloat) - the y position of the center point of the circle
 *	radius (GLFloat) - the radius that the painted circle will have
 */
void drawHollowCircle(GLfloat x, GLfloat y, GLfloat radius){
	int i;
	int lineAmount = 100; //# of triangles used to draw circle
	
	//GLfloat radius = 0.8f; //radius
	GLfloat twicePi = 2.0f * PI;
	
	glBegin(GL_LINE_LOOP);
		for(i = 0; i <= lineAmount;i++) { 
			glVertex2f(
			    x + (radius * cos(i *  twicePi / lineAmount)), 
			    y + (radius* sin(i * twicePi / lineAmount))
			);
		}
	glEnd();
}

Nice

Thank you for this share.
my question, how I can draw a number in centre of the circle ?