Programming in C · topic
Base and recursive cases, stack frames, tracing prints placed before and after recursive calls, call trees, recursion depth, recurrences for the number of calls, memoisation, tail recursion and mutual recursion.
A function is recursive when it calls itself, directly or through other functions. Recursion expresses a problem in terms of smaller instances of the same problem: the factorial of n is n times the factorial of n-1; a binary tree is a root with two smaller binary trees.
For a short recursive C function there are four things to determine: what it prints, what it returns, how many times it is called (or how many times some line runs), or what a variable holds afterwards. Each has a reliable mechanical method.
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