GlutKeyboardFunc callback doesn't work in openGL - glut

Question

I am trying to simply quit the application on pressing a key in openGL and the keyboard doesn't seem to work.
Neither am I am not able to quit the application just by clicking on the close button of the window. Any explanation for this behaviour? I am not recreating the window continuously either.
Here's the code snippet
void keyboardfunc(unsigned char key, int x, int y) {
cout << "Inside" ;
switch (key) {
case 'q': exit(0);
default: break;
}
int main(int argc,char ** argv)
{
.
.
.
glutReshapeFunc(reshape_func);
glutDisplayFunc(draw);
glutKeyboardFunc(keyboardfunc);
myinit();
glutMainLoop();
return 0;
}
The program is to simulate insertion sort by representing the array graphically , using a for loop I am clearing the screen every time and representing the numbers as histogram each time
Just to be clear the simulation of insertion sort works , only the keyboard callback doesn't work.

Answer 1

Your draw functions take the CPU control and don't let to execute GLUT events loop. Take into account that GLUT is single thread.
You must register a timer. Timer will produce new rendering. Each second compute next iteration and force to redraw scene.
void draw(){
renderHistogram();
}
void timer(int value) {
getNextIteration();
glutPostRedisplay();
glutTimerFunc(1000, timer, 1); // executed on a second
}
To register timer include this line before glutMainLoop:
glutTimerFunc(1000, timer, 1); // executed on a second
next iteration function would be:
int i = 0, j = 0;
void getNextIteration()
{
if (i == n) {
// Array is sorted
return;
}
int key;
key = arr[i];
if (j == 0 || arr[j] <= key) {
// Internal loop finished, reset j, and advance i;
arr[j + 1] = key;
i++;
j = i - 1;
}
arr[j + 1] = arr[j];
j = j - 1;
}