Display 3d point

Question

I am trying to display 3d point (50,30,20) using opengl but noting is displayed on the screen. How can I solve it?

init:

void init()
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(20.0, 70.0, 10.0, 40.0, 10.0, 30.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
 

}

Display:

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);
    glPointSize();
    glBegin(GL_POINTS);
    glVertex3f(50.0, 30.0, 20.0);
    glEnd();
    glFlush();
    glutSwapBuffers();
}

Answer 1

Your point is clipped by the near plane of the orthographic projection:

glOrtho(20.0, 70.0, 10.0, 40.0, 10.0, 30.0);

glVertex3f(50.0, 30.0, 20.0);

The OpenGL coordinate system is a right handed system (see Right-hand rule). In view space the y axis points upwards and the x axis points to the right. Since the z axis is the Cross product of the x and y axis, it points out of the view.
Hence you've to shift the point along the negative z axis in between the near and far plane:

glVertex3f(50.0, 30.0, 20.0);

glVertex3f(50.0, 30.0, -20.0);