How to get info from main to void?

Question

I have been tasked with using GLUT to ask the user to enter coordinates and display a rectangle. However, I can't seem to get the coordinates from "int main" to "void display".

Here is my code so far:

#include<iostream>
#include<gl/glut.h>

using namespace std;
void display(float yaxis, float xaxis)
{
    glClearColor(1, 1, 1, 1);

    glClear (GL_COLOR_BUFFER_BIT);

    glBegin (GL_QUADS);

    glColor3f(0, 0, 0);

    glVertex2f(yaxis, -xaxis);
    glVertex2f(yaxis, xaxis);
    glVertex2f(-yaxis, xaxis);
    glVertex2f(-yaxis, -xaxis);
    glEnd();

    glFlush();

}
int main(int argc, char** argv)
{
    float xaxis;
    float yaxis;

    cout << "Please enter the co-ordinates for the x axis and press enter.";
    cin >> xaxis;
    cout << "You entered: " << xaxis
            << ".\n Please enter the co-ordinates for the y axis and press enter.";
    cin >> yaxis;
    cout << "You entered: " << yaxis << ".\n Here is your rectangle.";

    glutInit(&argc, argv);

    glutInitWindowSize(640, 500);

    glutInitWindowPosition(100, 10);

    glutCreateWindow("Triangle");

    glutDisplayFunc(display);

    glutMainLoop();
    return 0;
}

Answer 1

glutDisplayFunc function has the following declaration:

void glutDisplayFunc(void (*func)(void));

Therefore you can't use your display function as you implemented it. Here is an quick example that can fix your error:

#include<iostream>
#include<gl/glut.h>

using namespace std;
static float yaxis;
static float xaxis;
void display()
{
    glClearColor(1, 1, 1, 1);

    glClear (GL_COLOR_BUFFER_BIT);

    glBegin (GL_QUADS);

    glColor3f(0, 0, 0);

    glVertex2f(yaxis, -xaxis);
    glVertex2f(yaxis, xaxis);
    glVertex2f(-yaxis, xaxis);
    glVertex2f(-yaxis, -xaxis);
    glEnd();

    glFlush();

}
int main(int argc, char** argv)
{
    cout << "Please enter the co-ordinates for the x axis and press enter.";
    cin >> xaxis;
    cout << "You entered: " << xaxis
            << ".\n Please enter the co-ordinates for the y axis and press enter.";
    cin >> yaxis;
    cout << "You entered: " << yaxis << ".\n Here is your rectangle.";

    glutInit(&argc, argv);

    glutInitWindowSize(640, 500);

    glutInitWindowPosition(100, 10);

    glutCreateWindow("Rectangle");

    glutDisplayFunc(display);

    glutMainLoop();
    return 0;
}