Help concatenate variables

hi everybody, maybe someone can help me.
my problem is:
I have a number of checkboxes, which are keys with the following code :
key1.onRelease = function() { myVar1 = “1”};
key2.onRelease = function() { myVar2 = “16”}
key3.onRelease = function() { myVar1 = “24”};…etc
variables are numbers 0-6,
I want to display in a dynamic textfield all these values in order, that means
the return must be : 11624…
I have tryed with :
myCode = myVar1+myVar2+myVar3+…, myCode is the var name of the dynamic textfield, but the result is NaN in FP8 and 0 in FP6. where is the mistake, or how must I proceed? thank you in advance.