OpenGL Program with Bizzaro Behaviour

[Icetigris]

I'm learning OpenGL for a class and for the lulz and I'm trying to write a program that does the following:

-Open a 500x500 window with a 10x10 grid of black squares with a 1 pixel white border around them. (done, works)
-Make the window resize without it going wonky. (done, works)
-When you click on a square, it changes colour. (broken)

When you click on a square, it will sometimes make a square change colour somewhere else on the grid. Only the bottom-leftmost square will change colour when you click on it.

I know it's a problem with the coordinate system, but I have no idea how, why, or where in my code this is happening. Can someone help me figure out where the problem is?

My code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <windows.h>  // Header File For Windows
#include <gl\gl.h>	  // Header File For The OpenGL32 Library
#include <gl\glu.h>	  // Header File For The GLU32 Library
#include <gl\glut.h>  // Header File For The GLUT32 Library
#include <gl\glaux.h> // Header File For The GLaux Library

//  Initial display-window size.  
GLsizei winWidth = 500, winHeight = 500;  
GLfloat red[10][10];
GLfloat green[10][10];
GLfloat blue[10][10];
GLuint gridSquare;

void drawQuads(void)
{
    GLint i, j;
	int m = 0;
	int n = 0;
    glBegin(GL_QUADS);	// Draw some quads!
    for(i = 0; i < winWidth; i=i+(winWidth/10))
   {
      for(j = 0; j < winHeight; j=j+(winHeight/10))
      {
        glColor3f (red[n][m], green[n][m], blue[n][m]);   //  Set fill color for quads to black.
        glVertex2i(i+1, j+1);					// Top Left
        glVertex2i((i+(winWidth/10)), j+1);			// Top Right
        glVertex2i((i+(winWidth/10)), (j+(winHeight/10)));	// Bottom Right
        glVertex2i(i+1, (j+(winHeight/10)));			// Bottom Left

        n++;
      }
    m++;
   }
	glEnd();			// Done Drawing The Quads
	
        glFlush ( ); //Process, OpenGL. DO IT NOW.
	printf("Done with drawQuads\n");
}

void init(void)
{
	glClearColor (1.0, 1.0, 1.0, 0.0);   //  Display-window color = white.
	for(int x = 0; x < 10; x++)
	{
		for(int y = 0; y < 10; y++)
		{
			red[x][y] = 0.0;
			green[x][y] = 0.0;
			blue[x][y] = 0.0;
		}
	}

	 printf("Done with init\n");
}

 void winReshapeFcn (int newWidth, int newHeight)
 {
	winWidth = newWidth;
	winHeight = newHeight;

    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ( );
    gluOrtho2D (0.0, (GLdouble) newWidth, 0.0, (GLdouble) newHeight);
	glViewport(0, 0, newWidth, newHeight);

    glClear (GL_COLOR_BUFFER_BIT);
	printf("Done with winReshapeFnc\n");
 }

void mouseFunc(GLint button, GLint action, GLint xMouse, GLint yMouse)
{
	if(action == GLUT_UP)  
	{  double w, h, width, height = 0.0; 
		int squareX, squareY = 0; 
		width = winWidth; 
		height = winHeight;  

		w = width/10; 
		h = height/10;
     
		yMouse = winHeight - yMouse;
		
		printf("Mouse click at %d, %d\n", xMouse, yMouse); 
		squareX = (int)(xMouse/w); 
		squareY = (int)(yMouse/h); 
		
		red[squareX][squareY] = .5;
		green[squareX][squareY] = .5;
		blue[squareX][squareY] = .5;

		printf("R: %d G: %d B: %d\n", red[squareX][squareY],green[squareX][squareY],blue[squareX][squareY]);
		printf("squareX: %d, squareY: %d\n",squareX,squareY);
		glutPostRedisplay();
 
		printf("Done with mouseFunc\n");
	}
	

}

 void main (int argc, char** argv)
 {
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition (100, 100);
    glutInitWindowSize (winWidth, winHeight);
    glutCreateWindow ("The GRIDS that is killing ED");

	init ( );
    glutDisplayFunc (drawQuads);
    glutReshapeFunc (winReshapeFcn);
	glutMouseFunc(mouseFunc);

    glutMainLoop ( );
 }