Function and Variable Problem

Hi Everyone,

Its been a while since Ive played with flash but Im trying to make a menu that when someone clicks on a university, the university appears and when they click on it again, it disappears.

movieVar = 0

mcUni.onEnterFrame = function()
{
uniMenu(mcCov, movieVar, mcContent.mcUni);
}

uniMenu = function (cover, movieVar, uni)
{
cover.onRelease = function ()
{
if (movieVar == 1)
{
uni._visible = false;
movieVar–;
}
else if(movieVar == 0)
{
uni._visible = true;
movieVar++;
}
}
}

The problem is the movieVar never outputs and doesnt appear to update and wont switch on and off when I click the button. it will switch on, but not off.

Any help?