CECS282 - Lab 4 - Solved

Reading
Reading from C++ How to Program:

1.    Skim Chapter 9 for review of declaring classes and objects

2.    Chapter 10.1, 10.3, 10.4, 10.5, 10.6, 10.7 (operator overloading)

Assignment
There are two ways to get credit for this Lab. Either demo your Project 1 code and pass the demo; or complete the questions below. If you have not nished Project 1, you can also demo your PrintBoard and InBounds functions to get a 1-week extension on the due date.

1.    Suppose a C++ class has a eld (instance variable) of type string. You want to add a method to the class to access that string by returning it. You have four options for how to return the string; for each option, justify why you might choose to return in that way. One example is given:

(a)     string *

Answer: We might return a pointer if we want someone else to be able to mutate our eld, and they should know the eld might sometimes be null.

(b)     string &

(c)     string

(d)     const string &

2.    Answer True or False for each of these questions about operator overloading. Give a one-sentence explanation for each false answer.

(a)     The precedence (order of operations priority) of an operator cannot be changed by overloading.

(b)     If you overload operator==, the compiler automatically knows how to evaluate the != operator.

(c)     An operator can be a member operator only if the left-hand side operand is of a di erent type than the class it is de ned in.

(d)     You can modify the behavior of an operator that operates solely on primitive types, e.g., you can change the behavior of + when used with ints.

(e)     An arithmetic operator like operator+ must return an object of the same type as the parameters. (f) You should overload every operator for every class you write.

3.    Suppose you have two variables a and b of some arbitrary class C, and that C provides correct overloads for operators < and ==. Using only those two operators, and other boolean logic operators (and, or, not), show how to accomplish the equivalent of these conditional expressions. One example is given.

(a)     a <= b

Ans: (a < b || a == b)

(b)     a != b

(c)     a > b

(d)     a >= b

4.    Practice writing C++ classes by creating the following class. Separate the declaration into a .h le and the implementation of any non-inline methods into a .cpp le:

The class is named BankAccount and represents an account of money at an arbitrary bank. Satisfy these requirements:

(a)     Two elds: an account number (integer) and a balance (the amount of money in the account; a oating-point number).

(b)     One constructor, taking parameters for the accout number and balance of the account, and initializing the object appropriately.

(c)     One accessor method for the account balance, GetBalance().

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(d)     A method GetInterestRate(), which returns the interest rate of the account. Interest rate is equal to 0.001 if the account balance is less than 10,000; equal to 0.003 if balance is between 10,000 and 100,000 (inclusive); and equal to 0.005 if greater than 100,000.

(e)     A method ApplyInterest(), which multiplies the current balance by the account’s interest rate, and then increases the balance by that product.

(f)      A member operator operator<, which takes another BankAccount as a parameter and returns whether the context BankAccount (this) has a smaller balance than the parameter.

You must mark methods as const when appropriate, and must justify whether each parameter to your methods should be a copy, a reference, a pointer, or a const reference.