OpenGL - Moving Object By Mouse

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

#include <iostream>

using namespace std;

void init();
void display();

float a = 200.0, b= 200.0;

void setPoint(float x, float y){
    glColor3f(1.0, 0.0, 0.0);
    glBegin(GL_POINTS);
        glVertex2f(x,y);
    glEnd();
}

void init(){
    glClearColor(1.0,1.0,1.0,1.0);
    gluOrtho2D(0.0, 400.0, 0.0, 300.0);
}

void display(){
    glClear( GL_COLOR_BUFFER_BIT);
    glPointSize(10.0);

    setPoint(a,b);

    glFlush();
}

void mouse(int mouse, int state, int x, int y){
    switch(mouse){
        case GLUT_LEFT_BUTTON:
            if(state == GLUT_DOWN){
                cout << x << " -> " << y << endl;
                a = x/1.0;
                b = 300.0 - (y/1.0);

                glutPostRedisplay();
            }
        break;

    }

}

int main(int argc, char* argv[]){
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowSize(400,300);
    glutInitWindowPosition(200,100);
    glutCreateWindow("OpenGL Program");

    init();
    glutDisplayFunc(display);
    glutMouseFunc(mouse);

    glutMainLoop();

    return 0;

}

OpenGL - Moving Object By Mouse