Changing global variables

I’m trying to create a global variable that initially stores a 0.
Then via a function will change the value of that global variable, and allow the other functions to access the new number. I have it working where it adds 1 to the variable, and stores the number 1 however, I cannot get the number to add up beyond 1.

I have this in my first layer,frame.

_global.thisSound = 0;
function PlaySound(){
temp = _global.thisSound;
_global.thisSound = eval(temp) + 1;
}

Please note this is the basics of this function, there are other parts to the function for playing sounds, but this is the only part that I’m having the problem