I don't follow your explanation. main can't be in a loop ... do you mean there is a while(1) in main? How and when is Knipper called?

Do you have a simulator? Try following execution through with that to see what your code is doing.

As you have written it, teller will be 0 (or whatever value the compiler chooses, you didn't initialise it) every time Knipper is called. That's part of your problem - teller is an uninitialised auto variable.

You need:

static teller = 0;

now teller will maintain it's value between calls to Knipper()