CS 1320 (Principles of Algorithm Design I):
Homework #9

Assigned:: November 24, 1999.
Due:: December 6, 1999, at start of class.
Credit:: 30 points.

Programming problems

Credit:

10 points each.

Instructions:

Write a C++ program to solve each of the problems below. For each program, unless otherwise instructed, turn in:

A printed listing of your program. It should begin with comments giving your name, the assignment number, and a description of what the program does in terms of its inputs and outputs. If you make choices or assumptions in writing the program, this is the place to mention them. If your program consists of more than one function, precede each function (either its prototype or its definition) with comments explaining its purposes, parameters, and return value.
If the program requires input, the input(s) you used to test it.
Your program's output, when executed with the input(s) you used to test it.

See the guidelines for programming assignments for a more detailed description. Remember that at least one other human will read your program, so try to make it clear and readable. See the guidelines for tips on what makes for readable code, and the sample programs for examples.

Revised timesheets program

Ms. Gotta Haveit Now was very pleased with your work on the timesheet program (Homework #7). Tuesday, she attended the meeting of the Java Users Group of San Antonio and thought to herself that using a class to deal with times would simplify the code and improve its maintainability. She hires you to rewrite the code to use a time class.

For a description of what the program should do, see the problem description in Homework #7. Ms. Now wants you to create a Time class and then use Time objects in the program. To improve the code's maintainability, she really likes private members, both data and functions. Also, remember how she muttered "I hate reference variables. A mark of a good programmer is to use them only when necessary." You succeeded last time in avoiding unnecessary reference variables; try to do it again.

Hints

When creating the Time class, ask yourself what the class needs to do and what a Time object needs to store.
Some classes (including perhaps the Time class) do not need constructors or destructors. Writing your own constructor is useful only if you need to specify an object's state when creating it. Writing your own destructor is necessary only if some action needs to be taken when an object is destroyed; the example presented in the checkingAcct class was a gratuitous example.
It is possible to write the program using reference parameters only for passing stream objects. Do so.
You can write a function to subtract two different times (it might need to be a friend function of the Time class). Or you might try writing a member function decreasing a Time object's value by the value of another Times object.
You may start from your own solution to the previous homework or from the sample solution. For this problem, you should need to write very little new code; most of what you need to do can be done by rearranging existing code.

Recursive functions

Write a recursive function for each of the computational tasks described below. Also write a main program to test your function, such that someone could use this program to perform a variety of tests on the function. (See the recursive examples linked from the sample programs page for examples of such main programs.) Note: To receive full credit, your function must be recursive.

Summing numbers read from a file

Write a recursive function to return the sum of integers read from a file. For example, if the file contains the following lines

the function should return 100. You can assume that the calling program has opened the file. Your function should not print anything; it should just return the sum for the calling program to print.

Scaling an array

Write a recursive function to multiply every element of an array of doubles by a scaling factor (another double). For example, if the elements of the array are as follows:

and the scaling factor is -2, the function should change the elements of the array to the following:

Your function should not print anything; printing should be done by the calling program.