Opengl program to demonstrate hierarchical menus

2. Write an opengl program to demonstrate the hierarchical menus, to draw a rectangle and to increase or decrease the size of the rectangle?
/*
 * menu.c
 *
 *  Created on: Dec 16, 2013
 *      Author: kamath
 */
#include<GL/glut.h>
GLsizei wh=500,ww=500;
GLfloat size=3.0;

void display()
{
glFlush();
}

void myInit()
{
    glViewport(0,0,ww,wh);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);
    glMatrixMode(GL_MODELVIEW);
    glClearColor(0.0,0.0,0.0,1.0);
    glColor3f(1.0,0.0,0.0);
}

void myReshape(GLsizei w,GLsizei h)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0,(GLdouble)w,0.0,(GLdouble)h);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glViewport(0,0,w,h);
    ww=w;
    wh=h;
}

void drawSquare(int x,int y)
{
    y=wh-y;
    glBegin(GL_POLYGON);
    glVertex2f(x+size,y+size);
    glVertex2f(x-size,y+size);
    glVertex2f(x-size,y-size);
    glVertex2f(x+size,y-size);
    glEnd();
    glFlush();
}

void size_menu(int id)
{
    switch(id)
    {
    case 2: size=size*2;
            break;
    case 3:if(size>1) size=size/2;
    break;
    }
    glutPostRedisplay();
}

void top_menu(int id)
{
    switch(id)
    {
    case 1:exit(0);break;
    }
    glutPostRedisplay();
}

void myMouse(int button,int state,int x,int y)
{
    if(button==GLUT_LEFT_BUTTON&&state==GLUT_DOWN)
    drawSquare(x,y);
    if(button==GLUT_RIGHT_BUTTON&&state==GLUT_DOWN)
        exit(0);
}

int main(int argc,char **argv)
{int sub_menu;
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowSize(500,500);
    glutCreateWindow("Hierarchical Menus to Draw Squares");
    glutDisplayFunc(display);
    myInit();
    glutMouseFunc(myMouse);
    sub_menu=glutCreateMenu(size_menu);
    glutAddMenuEntry("Increase Square Size",2);
    glutAddMenuEntry("Decrease Square Size",3);
    glutCreateMenu(top_menu);
    glutAddMenuEntry("Quit",1);
    glutAddSubMenu("Resize",sub_menu);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
    glutReshapeFunc(myReshape);
    glClear(GL_COLOR_BUFFER_BIT);
    glutMainLoop();
    return 0;
}

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