if statement

Can someone explain why the following if statement does not execute when I change the variable 'a' in the active command line?

var a = 10;

if (a != b) {
	var b = a;
	var c = 1;
	var d = 1;
	var e = 1;
	var f = b+c+d+e;
}

I'm sure I had it working at some point but I forgot to save what I was doing!!!