Introduction

The lab assignment this week will introduce the use of void functions and command-line arguments.

Step 1: Getting ready

Recall what environment you set up in lab 1. Either through a graphical file system explorer or through the terminal:

1. Navigate to your cs16 directory:
   • For example, from the terminal:

   $ cd cs16

2. Create and navigate to the lab3 directory:
   • From example, from the terminal:

   $ mkdir lab3
   $ cd lab3

Step 2: Create and edit your C++ programs

This week you will create 2 files called change.cpp and calculate.cpp. Each corresponds with the problems listed below. Each is worth 50 points and should be solved in its own file. Both must be submitted for full assignment credit.

Program 1: change.cpp

Write a program that tells what coins to give out for any amount of change from 1 cent to 99 cents. For example, if the amount is 86 cents, the output would be something like the following:

86 cents can be given in 3 quarters, 1 dime, 1 penny.

Use coin denominations of 25 cents (quarters), 10 cents (dimes), and 1 cent (pennies) only. Do not use nickel and half-dollar coins.

Your program should use the following function (it doesn’t have to be the only function, but you have to use this one). Your program must use the compute_coins function declaration shown here:

void compute_coins(int amount);
// Precondition: 0 < amount < 100
// Postcondition: The function prints out the number of 
// quarters, dimes, and pennies needed to make the 
// amount value.

The program should verify that the value of amount is between 1 and 99 (inclusive). If this not the case, the function should print out an error message (see example below).

A loop in the program should have the user repeat this computation for new input values until the user enters a zero to quit.

A session should look exactly like the following example (including whitespace and formatting) with all manner of different numbers for the input.

$ ./change
Enter number of cents (or zero to quit):
86
86 cents can be given in 3 quarters, 1 dime, 1 penny.
Enter number of cents (or zero to quit):
99
99 cents can be given in 3 quarters, 2 dimes, 4 pennies.
Enter number of cents (or zero to quit):
1
1 cent can be given in 1 penny.
Enter number of cents (or zero to quit):
101
Amount is out of bounds. Must be between 1 and 99.
Enter number of cents (or zero to quit):
0

Important: Note that the words and the punctuation (commas, especially) can be different for different kinds of input values. They have to match the numbers, so singulars for “quarter”, “dime”, and “penny”, and plurals for “quarters”, “dimes”, and “pennies”. The autograder will not tolerate bad grammar!

Hints: It will be helpful to use lots of if-else statements and you will have to include the <string> library to make variable message to meet the singular/plural and comma/no-comma requirements.

Program 2: calculate.cpp

You will write program that mimics a simple calculator that can do one of three operations on two integers: addition, multiplication, or modulo.

The program takes 3 arguments at the command line: an integer, a character, and another integer. All of these arguments must be separated by a space character. The middle character can only be 1 of 3 choices: +, x, or %. The program then returns either the sum, the product, or the modulo of the 2 integers, respectively.

The program should be able to verify that:

1. the user has provided exactly 3 command-line arguments
2. the operator used is one of the 3 allowed operators and nothing else, and
3. when using modulo, the second integer is not zero (otherwise you would divide by zero)

For each of these conditions, the program should print out a specific error message (called the “usage” message) and exit. For each condition listed above, the error messages should respectively be:

1. Number of arguments is incorrect.
2. Bad operation choice.
3. Cannot divide by zero.

Hint: You have to use cerr instead of cout to output the usage messages. Do not use cerr for any other outputs the program makes. While cerr and cout are alike in that they direct values to standard output, we usually use cout for the standard output, but use cerr to show or report errors to the user and the system.

You may use the exit(1) statement when exiting from giving some of the error messages.

Here is a skeleton program to help get you started.

// calculate.cpp
// By: <your name here>

#include <iostream>
#include <cstdlib>
using namespace std;

// Usage: ./calculate int char int
// char can either be: + x or %
int main(int argc, char *argv[]) {
    // PART 1: Check to see if the number of arguments is correct
    //         Hint: use "if (argc ...)" to check this,
    //         use cerr to output any messages

    // PART 2: Convert arguments into integers (only those that need it!)
    //         Hint: this means using atoi()

    // PART 3: Check for illegal operations like divide by zero...
    //         use cerr to output any messages

    // PART 4: Do the appropriate calculation,
    //         outputs using both cout and cerr

    return 0;
}

This program does not loop back to take inputs again. Your outputs should match the ones in the example run shown below.

$ ./calculate 4
Number of arguments is incorrect.

$ ./calculate 1 + 2
3

$ ./calculate 7 x -5
-35

$ ./calculate 4 - 3
Bad operation choice.

$ ./calculate 14 % 0
Cannot divide by zero.

Step 3: Create a makefile and compile the code

In order to learn another way to manage our source code and their compilations, we will create a makefile and put the usual g++ commands in it. Afterwards, whenever we want to (re)compile our programs, the Linux command make is a lot shorter—so this is a convenience. The use of makefiles will be very useful the more complex our programs and CS projects become. We will discuss make and makefiles in class soon!

Using your text editor, create a new file called makefile and enter the following into it:

all: change calculate

change: change.cpp
    g++ change.cpp -o change

calculate: calculate.cpp
    g++ calculate.cpp -o calculate

Then from the terminal, you can issue a command for either program, like so:

$ make change

Or,

$ make calculate

Or, you can issue one command that will compile both projects mentioned in the makefile.

$ make

If the compilation is successful, you will not see any output from the compiler. You can then run your programs. For example,

$ ./change

If you encounter an error, use the compiler hints and examine the line in question. If the compiler message is not sufficient to identify the error, you can search online to see when the error occurs in general.

Remember to re-compile the relevant files after you make any changes to the C++ code.

Step 4: Submit your programs for grading

Once you are satisfied your programs are correct, then it’s time to submit them. While working with others is OK, you still must submit your own lab. Even if you’re working with another person, do not copy each other’s code.

Log into Gradescope and select CMPSC 16 under Summer 2021, and navigate to the Lab 3 assignment. Then click on the “Upload Submission” button on the bottom right corner to make a submission.

You will be given the option of uploading files from your local machine or submitting code from a GitHub repo. Follow the steps to upload both source files to Gradescope (do not upload any other files). If your files do not have those exact names as presented in this lab, the autograder will not grade them. You can resubmit your files as many times as you like before the assignment deadline.