I suggest you converge your problem code toward the sample I gave. If your problem remains at the end of that process, post the code and we will help further.

Your immediate problem is likely to be that you are indexing an element that wasn't present in the array, so it is being created for you and set to undef. It is not clear from your code where $t may be set to anything other than 0, but it seems likely in your "real" code that it is.

Again I suggest that you reproduce the problem in a small sample application (see my sample as a guide) that we can run and check.