Draw moving Circle

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <cmath>

void init()
{
    glClearColor(0, 0 , 0 , 0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0, 20.0, 0.0, 20.0 );
    glMatrixMode(GL_MODELVIEW);
}

void drawCircle(int r, int x_center, int y_center)
{
    int deg =0;
    double theta, x, y;

    glBegin(GL_POLYGON);
    while (deg<360)
    {
        theta = (deg*M_PI)/180;

        x = r*cos(theta) + x_center;
        y = r*sin(theta) + y_center;
        deg++;

        glVertex2d(x , y);
    }
    glEnd();
}

int angle= 0;
void display()
{
    glClear(GL_COLOR_BUFFER_BIT);

    glColor3ub(255,255,255);
    drawCircle(3, 5, 5);

    glPushMatrix();
    glColor3ub(0,0,0);
    glTranslatef(5,5,0);
    glRotatef(angle, 0, 0, 1);
    glTranslatef(-5,-5,0);
    glLineWidth(2.0);
    glBegin(GL_LINES);
    glVertex2i(2,5);
    glVertex2i(8,5);

    glVertex2i(5,2);
    glVertex2i(5,8);
    glEnd();
    glPopMatrix();

    glFlush();

}
void update(int value)
{
    angle -= 10;

    glutPostRedisplay();
    glutTimerFunc(50,update, 0);
}


int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB);

    glutInitWindowPosition(300,200);
    glutInitWindowSize(500,500);

    glutCreateWindow("Circle");
    glutDisplayFunc(display);
    glutTimerFunc(0,update, 0);
    init();
    glutMainLoop();

    return 0;

}