OpenGL - Drawing Triangle

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

#include <iostream>
using namespace std;

#define LIMIT 10.0      // limit

// prototype
void setup();   // initialization of the program
void display(); // drawing method
void createCoordinate();  // certasian coordinate
void draw();    // draw the object

void setup(){
    glClearColor(1.0, 1.0, 1.0, 1.0);
    gluOrtho2D(LIMIT - 11, LIMIT, LIMIT - 11, LIMIT); // -x1, x2, -y1, y2
}

void display(){
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 0.0, 0.0);

    draw();
    createCoordinate();

    glFlush();
}

void draw(){

    // vector defining
    GLfloat one[] = {0.5, 0.5};
    GLfloat two[] = {0.5, 5.0};
    GLfloat three[] = {5.0, 5.0};

    glBegin(GL_POLYGON);
        glVertex2fv(one);
        glVertex2fv(two);
        glVertex2fv(three);
    glEnd();

}

void createCoordinate(){
    glBegin(GL_LINES);
        // horizontal lines
        glVertex2f(-LIMIT, 0.0);
        glVertex2f(LIMIT, 0.0);

        // vertical lines
        glVertex2f(0.0, -LIMIT);
        glVertex2f(0.0, LIMIT);
    glEnd();
}

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

    setup();
    glutMainLoop();

    return 0;
}

OpenGL - Drawing Triangle