ESc 014

Lab 7 -- Currency Converter
Thursday, May 23, 2002

Objectives

To practice writing a class
To gain experience working in the UNIX operating system environment

Introduction

This week, you'll gain some experience working with the UNIX operating system. Unlike Windows, UNIX is command-line based, which means you interact with it mainly through keyboard commands instead of the mouse. You'll be referring to your "UNIX for Dummies" reference guide throughout this lab.

Setup

UNIX is running on the computer named blackduck which is where you've been transferring your starter code from all these past weeks. This time, though, you'll login to blackduck and work directly from there. Follow these steps:

On your desktop is an icon for "SSH Secure Shell Client" (NOT "SSH Secure File Transfer Client"). Launch it.
From the File menu, click "Quick Connect".
Type in blackduck.union.edu for the Host Name, and then the same username you've been using whenever you transferred files from blackduck previously. Press the "Connect" button.
Type in your blackduck password (not your regular email password)
You should now be logged in to your account on blackduck. Lots of information about the machine's status should have quickly scrolled by on the screen and then a prompt (a cursor) appears at the bottom of the window. It is awaiting your next command. The prompt where the cursor is should have your username next to it. This is your home directory. It's the one you always start in whenever you log into blackduck.
Look up "ls" in your UNIX reference guide. This is how you view the files in your current directory. Try using the command to see what files and directories you have in your home directory. Note that regular files appear in black while directories appear in either light or dark blue. (Remember, a directory in UNIX is like a folder in Windows). You can use options too. The "-l" option (that's lower-case letter "l") will list details about your files. Try it by typing "ls -l" (without the quotes) and see what happens. Try some of the other options listed in your guide.
One of the directories you should see after typing "ls" should be the "esc014pub" directory. This is the one you've been going to in previous labs to get the starter code. You need to "open up" this directory to get at what's inside by using the cd command to change directories. Look it up in your reference guide now. Then use it to move to the "esc014pub" directory by typing
```
cd esc014pub
```
Your prompt should change to reflect the new directory you're in.
Look at the contents of this "esc014pub" directory (using ls). One of them should be named "lab7". That's the directory that contains the files you need. We want to copy that folder and all of its contents back to your home directory so you can work with your own personal copy. You can do this with the cp command which stands for "copy". Type
```
cp -R lab7 ~
```
This will copy the lab7 directory and everything in it to ~ (the tilde character -- it should be in the upper-left of your keyboard underneath the esc key). What's ~? It's UNIX shorthand for your home directory. What's that -R for? Look up "cp" in your reference guide now. What does it say about -R and why did I need it?
Now that the copy is complete (we hope), we should be able to go back to our home directory and see if it's there or not. We're going to use "cd" again to change back to our home directory. Look it up in your guide again and learn how to get back to your home directory easily. Careful! Your home directory is different from
```
/home
```
which is a directory that happens to be named "home" (as opposed to your home directory which is named with your username). Once you've changed directories back to your home directory, list the contents and see if "lab7" is now a new directory in the listing. If so, it worked! Otherwise, try to perform the copy again or ask your instructor for help.
Type cd lab7 to change directories into your copy of lab7
Look at the files within it. There should be two. One is "yen.h" and the other is "yenTest.cpp". I have provided hard copies of both of these files so you can refer to them.
You'll be using a text editor called "pico" to write your code for this lab. "pico" is an easy-to-use editor described in your reference guide starting at the bottom of p. 124. Refer to it as you need to when writing your code.

Your Mission

Your job is to complete a program that uses a class called yenConverter to convert dollars into Japanese yen and back again.

Of the three files required to make this work, you only need to write one of them: the class file that contains the member function definitions. I've already written the header file (yen.h) and the tester file (yenTest.cpp) for you. You should not alter these files. The class file you will write will be named yen.cpp. You can begin editing a new file with this name by typing

pico yen.cpp

at the prompt. In addition to the commands given in the reference guide, you can also use the arrow keys on your keyboard to move the cursor around the screen in pico.

The Details

Take a look at the code in the header file (yen.h). Listed here in the "public" section are the prototypes for the member functions and comments explaining what the functions are supposed to do. The four functions you'll be writing will use and manipulate the two variables listed in the "private" section. convertToDollars is a boolean variable controlling the direction of conversion: from yen to dollars or vice versa. yenPerDollar is the exchange rate.

Once you've studied the comments and function prototypes in the header file, you should be able to write the function definitions in your new yen.cpp file. Classes present many new changes in syntax and meaning, so don't forget about these possible pitfalls:

Don't forget to type in the line that includes the code from "yen.h"
Remember to use the "double colon" notation for your functions.
When you write the constructor, remember its job: to simply initialize the private variables. What their initial values should be are listed in the header file.
Remember that member functions automatically receive access to the private variables listed in the header file. You don't need to redeclare them. You just use them!

Compiling and Debugging

Once you've finished your yen.cpp file, save it (Ctrl-O) and exit pico (Ctrl-X). The C++ compiler that blackduck has is named g++. You can type it followed by the names of the source code files (NOT the header file) to compile them. You can also specify the output file with the "-o" option (that's the lower-case letter "o"). So typing:

g++ yen.cpp yenTest.cpp -o yen

will compile the two source code files (including the header file because you included it, remember?) The resulting executable file will be output to a file called yen. If there are compiler errors, they will show up now. Just like Visual C++, some of the compiler errors will be direct and helpful and others will be cryptic. It should at least tell you what line the problem is on or near. If you get compiler errors, go back into yen.cpp with pico and fix them. When using pico to edit, you can press Ctrl-c to display the line number that your cursor is on so you can find your error. Then exit and recompile.

If no errors occur, a new command prompt will appear after you compile. Do an "ls" to check out your files. A new one should appear called yen. That's the completed program you can run! To run it, type

./yen

(that's a period, a slash, and then yen.) Hopefully, it'll work. As always, you should study the test file yenTest.cpp yourself to figure out by hand what the correct output should be.

How to turn in this lab

When you are done, you can logout of your blackduck account by typing

logout

Then use the file transfer program to transfer just the new file (yen.cpp) to your desktop. Upload it to BlackBoard and print out a hard copy. Don't forget your opening comment block!

Remember, you will be graded on the correctness of your implementation, neatness, presentation, style of your program code, thoroughness of your testing, and good use of the C++ language. It's important to comment your code where appropriate and to do little things like space things properly, use readable indentation, and also to make sure the overall design and logic of the program are coherent.

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