OpenGL not displaying the correct output when not running in cmd prompt

Question

I am trying to write a math education system for year 1 student. My goal is to have all the interaction run within a window. When I click on the first window, (+ window), all that appears is black window without any output, but in command prompt it runs fine.

#include "stdafx.h"
#include <stdlib.h>
#include <iostream>
#include <glut.h>
#include <time.h>

using namespace std;
GLfloat xrot;
GLfloat yrot;
bool mouseDown = false;
bool createWindow = false;

int m=0;
int n=0;
int num1=0;
int num2=0;
int counter=0;

//-------------------------------------------------------------------


void handleKeypress(unsigned char key,int x,int y)
{
    switch(key)
    {
        case 27:
        exit(0);
    }
}

void handleResize(int w,int h)

{

    glViewport(0,0,w,h);

    glMatrixMode(GL_PROJECTION);

    gluPerspective(45.0,(double)w/(double)h,1.0,200);

}

void idle()
{
if (!mouseDown)
{
xrot+= 0.3f;
yrot+= 0.4f;
}

glutPostRedisplay();
}

void drawScene1()

{

    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    glBegin(GL_QUADS);
    glColor3f(1.0,0.0,0.0);
    glVertex3f(-1.0f,5.0f,-20.0f);
    glVertex3f(-1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,5.0f,-20.0f);
    glEnd();

    glRotatef(90.0,0.0f,0.0f,1.0f);

    glBegin(GL_QUADS);
    glColor3f(1.0,0.0,0.0);
    glVertex3f(-1.0f,5.0f,-20.0f);
    glVertex3f(-1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,5.0f,-20.0f);
    glutSwapBuffers();


}

void drawScene2()

{

    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    glRotatef(90.0,0.0f,0.0f,1.0f);

    glBegin(GL_QUADS);
    glColor3f(0.0,0.0,1.0);
    glVertex3f(-1.0f,5.0f,-20.0f);
    glVertex3f(-1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,-5.0f,-20.0f);
    glVertex3f(1.0f,5.0f,-20.0f);
    glEnd();

    glutSwapBuffers();
}

void myInit(void)
{
glEnable(GL_DEPTH_TEST);
glClearColor(1.0, 1.0, 1.0, 0.0); // set the background to white
glColor3f(0.0, 0.0, 0.0);
// set the drawing color to black

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1000.0,1000.0,-1000.0,1000.0,-100.0,100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

}
//------------------------------------------------------

void triangle()
{
    glBegin(GL_TRIANGLES);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(0.0f,100.0f,0.0f);
    glVertex3f(100.0f,-100.0f,0.0f);
    glVertex3f(-100.0f,-100.0f,0.0f);
    glEnd();
}

void minus()
{
    glPushMatrix();
    glBegin(GL_QUADS);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(-200.0f,50.0f,0.0f);
    glVertex3f(-200.0f,-50.0f,0.0f);
    glVertex3f(200.0f,-50.0f,0.0f);
    glVertex3f(200.0f,50.0f,0.0f);
    glEnd();
    glPopMatrix();
}

void myDisplay(void)
{

// Clear Color and Depth Buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Reset transformations
    glLoadIdentity();

    // Set the camera
    gluLookAt(0, 0, 3, 0 , 0 , 0 , 0.0f,1.0f,0.0f);

    //Generate random number 
    srand (time(NULL));
    num1 = rand() % 10 +1; 
    num2 = rand() % 10 +1;
    if(num1 < num2){
    int temp = num1;
    num1 = num2;
    num2 = temp;
    }

    //rows and column
    m = 2;   //row
    n = 5;   //column

    counter=0; //make sure it zero

    //First Number to be draw
    glPushMatrix(); //set as origin
    glTranslatef( -700.0,700, 0 ); //translate
    //draw
    for(int i = 0; i < m; i++){ //row
        for(int j=0; j < n; j++) { //column
            if(counter>=num1) break; //a=how many triangle need to draw; s=already draw how many triangle; 
            glPushMatrix(); //set transformation
            glTranslatef( i*200.0 ,j*-200.0, 0 ); //translate
            triangle(); //draw triangle
            glPopMatrix(); //reset transformation
            counter++; //counter s
        }
    }
    glPopMatrix(); //reset transformation

    //create plus sign
    glPushMatrix(); //set transformation or object position/orientation/scale for reset
    glTranslatef( 0.0,400, 0 );
    minus();
    glPopMatrix(); //reset transformation to origin

    counter=0; //reset counter
    //Second number to be draw
    glPushMatrix();
    glTranslatef( 500.0,700, 0 );
    for(int i = 0; i < m; i++){
        for(int j=0; j < n; j++) {
            if(counter>=num2) break;
            glPushMatrix();
            glTranslatef( i*200.0 ,j*-200.0, 0 );
            triangle();
            glPopMatrix();
            counter++;
        }
    }
    glPopMatrix();

    //Control
    glutSwapBuffers();//take the drawing to the screen

    //check answer
    /*cout<<num1<<endl; //debug
    cout<<num2<<endl;*/

    int check=0;
    int answer=0;
    cout << "Answer ???"<<endl;
    cin >> answer;
    while(true){
        check=num1-num2;
        if(answer==check){
            cout << "CORRECT!!!"<<endl;
            break;
        } else{
            cout << "TRY AGAIN!!!";
            cout << "Answer ???"<<endl;
            cin >> answer;
        }
    }
}



void mouse (int button, int state, int x, int y){
    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN){
    myInit();
    triangle();
    minus();
    myDisplay();
    }
}


int main(int argc,char** argv)

{

    glutInit(&argc,argv);

    myInit();

    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);

    glutInitWindowSize(500,500);


    //window1=

     glutCreateWindow("First window");

    glutDisplayFunc(drawScene1);

    glutKeyboardFunc(handleKeypress);

    glutReshapeFunc(handleResize);
    glutMouseFunc(mouse);

    //create the second  window

    //window2 =

    glutCreateWindow("Second Window");

    //define a window position for second window

    glutPositionWindow(540,40);

    // register callbacks for second window, which is now current

    glutReshapeFunc(handleResize);

    glutDisplayFunc(drawScene2);

    glutKeyboardFunc(handleKeypress);
    glutMouseFunc(mouse);

    glutMainLoop();





    return 0;


}

Answer 1

You're mixing stdio (i.e. console input/output) with windowing system event processing. This is a recipe for problems. stdio operations block until they're finished. In the case of reading from cin the process will block, waiting for input from the console until a linefeed is entered. During this time no windowing events are processed and nothing drawn to the OpenGL window.

In short, you can't mix the two in the way you did. You can use output (cout and cerr) just fine, they will write to NIL if theres no console attached, but trying to read something will block indefinitely. You'll have to think of other ways than stdio to interact with your user in event-interactive programs. I.e. you've to process key events in the keyboard callback.