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Understanding Recursion in CS 105 - Fall 2009 Lab 11 Overview

In this lab, we explore the concept of recursion through various mystery functions. A recursive function can call itself with smaller arguments until reaching a base case. We focus on three mystery functions: mystery1, which tests numerical input; mystery2, which evaluates Boolean conditions with strings; and the more complex mystery3, which takes two integer parameters. Participants are encouraged to predict outcomes for specific inputs before testing them for accuracy. Stay tuned for midterm results and further announcements!

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Understanding Recursion in CS 105 - Fall 2009 Lab 11 Overview

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  1. CS105 Lab 11 – Recursion • Announcements • Midterm 2 may have been harder/longer than we had anticipated • We will grade Midterm 2 completely before making any further announcements • please watch this space! CS 105 – Fall 2009

  2. Objective: Understanding Recursion • A recursive function can call itself one or more times • with “smaller” arguments • General structure: Private Function recFunction(data As … ) As … If <base case condition> Then recFunction = <base case answer> Else recFunction = recFunction(smaller data) End If End Function Recursive function call CS 105 – Fall 2009

  3. Mystery Function 1 • Open lab11.xls and study the code for Mystery 1 • Predict what the answer will be for: • mystery1(5) • mystery1(6) • mystery1(7) • Now try it and see if you are correct! CS 105 – Fall 2009

  4. Mystery Function 2 • Mystery function 2 is more interesting: Private Function mystery2(strX As String) As Boolean • The data is of type String and the answer is of type Boolean (True/False) • We get “smaller” strings using the Mid function • Mid(string, startPosition, numberOfLetters) • Predict the answer for these cases, then check it: • mystery2(“A”) • mystery2(“Radar”) • mystery2(“radar”) CS 105 – Fall 2009

  5. Mystery Function 3 • Mystery function 3 is more complex: Function mystery3(intN, intM As Integer) As Integer • The first If condition is not a base case! • It is a recursive case • Predict the answer for these cases, then check it: • mystery3(5, 6) • mystery3(6, 5) • mystery3(2, 6) CS 105 – Fall 2009

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