I have coded circle and point as eye and i want the points to be moving up and down. Please how do I make it possible?

 * GLUT Shapes Demo
 * Written by Nigel Stewart November 2003
 * This program is test harness for the sphere, cone
 * and torus shapes in GLUT.
 * Spinning wireframe and smooth shaded shapes are
 * displayed until the ESC or q key is pressed.  The
 * number of geometry stacks and slices can be adjusted
 * using the + and - keys.

#include <windows.h>
#include <GL/glut.h>

#include <math.h> // needs to be included for cos and sin functions

using namespace std;

#define PI 3.1415926535898

void init(void)
    gluOrtho2D(0.0, 150.0, 0.0, 150.0);

GLint circle_points= 100;

void MyCircle2f(GLfloat centerx, GLfloat centery, GLfloat radius){ //function to draw circle

    GLint i; //declaring integer for the 'for' loop
    GLdouble theta;
    glBegin (GL_POLYGON); //begin drawing a polygon
    glColor3f(1.0f, 1.0f, 1.0f); // set color for the circle to a shade of red
        for(i=0; i<circle_points; i++){ //for loop to draw circle
            theta = 2*PI*i/circle_points; //value for theta or angle in radians
            glVertex2f(centerx+radius*cos(theta),centery+radius*sin(theta)); //draw vertices of circle
    glEnd(); //signifying end of the polygon in this case circle

void Display(void)
    //clear all pixels with the specified clear color
    glClearColor (0.2, 0.2, 0.7, 0.0);

    MyCircle2f(80.0, 85.0, 10.0); //calling the circle function and setting center to be point 80, 85 with radius of 10
                                // this is possible because all these functions are in the same project /class
    //the eyes are black points
    //set the point size to be 3.0 pixels

        glColor3f(0.0,0.0,0.0); //setting color of eye to black
        glVertex2f(77.0,88.0); //given that the center of the circle(head of human) is at point(80,85)
        glVertex2f(83.0,88.0); // creating a point 3pixels each from the center positions of the circle will achieve the
                            //the expected results that is the eye

    //polygonal body
    glColor3f(0.8,0.0,0.9);//setting the color for the polygon

        glVertex2f(75.0, 75.0); //this vertex is carefully placed(calculated) so that it is tangential to the circle(head)
                                //such that is starts 5 pixels/points to the left from the center but  10pixels/points down the y coordinates from the center
                                //since the radius is 10pixels or points
        glVertex2f(85.0, 75.0);  //this is also calculated with similar explanation as above. notice the y coordinates are the same (75) this gives a horizontal line to for the polygon

        glVertex2f(100.0, 30.0); //coordinate (100, 30) meaning it opens up to the right and comes down
        glVertex2f(60.0,30.0);   // coordinate (60, 30), meaning it opens up to the left and comes down at the same position as the y coordinate that is 30
                                //to form a horizontal line for the base of the polygon

    //rectangular legs
    glColor3f(1.0, 0.8, 0.1);   //color for legs
    glRectf(70.0, 5.0, 75.0, 30.0); //coordinates for rectangle
    glRectf(85.0, 5.0, 90.0, 30.0); //coordinates for rectangle

    //lines for hands
        glVertex2f(74.0, 70.0); //calculated and carefully placed
        glVertex2f(50.0, 50.0);

        glVertex2f(88.0, 70.0); //calculated and carefully placed
        glVertex2f(110.0, 50.0);

    glFlush(); //flush OpenGL and call to display buffer

int main(int argc, char *argv[])
    glutInit(&argc, argv);
    glutInitWindowSize(500, 500);
   glutInitWindowPosition(0, 0);
   glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);

   glutCreateWindow("Stick Figure");
   glutDisplayFunc(Display); //function call to display stick figure

   return EXIT_SUCCESS;