In this episode, we look at those mysterious alphabetic integer variables, otherwise known as resident integer variables. These special variables help boost the performance of the program, but they also need careful handling to make sense of what they're doing. We also look at the topic of "call by value" where a procedure can manipulate local copies of variables without changing the variable's global value.

RESOURCES: http://www.colinhoad.com/bbcmicro/cosmicinvaders/