Introduction to Computer Science

Quiz 6 Study Guide

This page contains a list of things you should know before taking Quiz 6. If you have any questions as to the correct answers to any of these questions, please let me know.

Recursion

Lab 09 dealt with recursive functions: those functions which call themselves. You should understand how recursive functions work and be prepared to write simple recursive functions without the aid of the computer. You should know how the stack works with recursive functions; in particular, you should understand that each recursive call generates an additional stack frame and that multiple stack frames for the same function can exist simultaneously.

Exercises

Write each of the following functions both iteratively and recursively. Remember: your recursive function should not include any for or while loops.

• A function summate which sums the numbers between 1 and a parameter n.
• A function factorial which multiplies the numbers between 1 and a parameter n.
• A function revstr which reverses a string.
• A function dupe_list which duplicates each element in a list (e.g. duplicate([1,2]) returns a new list [1,1,2,2]).

Draw a stack diagram of summate(3) when it reaches its base case.

Classes and Objects

The most recent lectures (and Lab 10) have dealt with classes and objects. You should know how to write a class, how to create an object, and how to call an object’s methods. You should understand the purpose of classes and objects and be prepared to write and debug simple classes without the aid of the computer.

Exercises

Answer the following questions:

• What is the difference between a function and a method?
• What is special about the __init__ method (also called the constructor)? When is it called?
• What is special about the __str__ method? When is it called?
• What is the difference between a class and an object?
• Why is object-oriented programming useful? That is, what is the advantage to using classes and objects rather than just writing programs using the Python we learned before classes and objects?

Write the following classes:

• A Die class which represents a six-sided die. It starts with a value of 6 and provides two methods: roll (which picks a new value for the die) and get_value (which returns the current value of the die).
• A BankAccount class which takes the owner of the account upon construction and sets the account balance to zero. This class should have a deposit method (to add money) and a check_balance method (to check the balance of the account).
• A Yoyo class which starts with 14 inches of string and a variable direction which is initially "down". This class should have a move method. If the object is moving down, the move method should subtract an inch of string. If the object has no more string, it begins moving "up"; a yo-yo moving "up" adds an inch of string. If the object has all 14 inches of string, move causes it to start moving "down" again.