ITPEC FE Morning October 2018 Question 8

A function using itself from within its body — that is what a recursive call is.

A recursive function solves a problem by calling itself on a smaller instance, such as n! = n × (n − 1)!, until it reaches a base case that returns without calling itself. Each call gets its own local variables and return address on the stack, so the calls unwind in reverse order.

Answer (a)

Why not others:

• •(b) — running processes in response to events rather than in a fixed order is event-driven processing
• •(c) — keeping a program in memory after it runs so it can be used again without reloading describes a reusable program, not recursion
• •(d) — undoing a failed process is rollback, as in transaction recovery

Key rule: A recursive routine calls itself and needs a base case to stop; it must also be reentrant, because each call keeps its own copy of the local data.

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