CS 112b
Spring 2004
Ileana Streinu

Lab 1

Introduction to C++

This lab will be spread over the week on Tu and Th, during the lecture and lab periods.

Read the whole lab before starting working on it, so that you know what you are required to do by the end of the lab.

Overview

Today you learn the basic routine for writing C++ programs, compiling them, executing and documenting the execution. You will do this for every homework and for many labs throughout the semester.
Make sure you know how to carry through each of these steps, otherwise seek help from me.

Log on to Novel, then log on the Unix machine beowulf under Windows, using ssh, or: Reboot the lab computer to Linux and log on to the class account directly from there.
Write your first C++ program, plus: Input/Output in C++, a small exercise
Use script to record a Unix session and show the compilation and execution of your program
Submit your work
Optional: Pipe in input data to your program from a data file.

Getting Started

This section will help you connect to the Linux server.

In Windows

Login to the Novell Tree using your student Novell account.
Launch an ssh window. You do this the way you learned in CSC111, or ask me if you do not know how. Connect to beowulf.csc.smith.edu.
When the login prompt to beowulf shows up, enter your 112b-xx account and password.
Change the password to something you remember easily and write it down. I will not be able to help you if you forgt your password.
Check your email: you should have received an email from the class account 112b. If not, please email me at 112b "at" cs.smith.edu to let me know that you should be added to the class mailing list.

In Linux

Turn off all programs and reboot your computer into Linux mode.
Log on to the system using your 112b class account.
Then use the shell windows to check your email using pine.

If this works, you will have the option of logging on and doing your work under any of the two environments (Windows or Linux). I strongly recommend that you get familiar with working directly under Linux.

Create a directory for each lab and homework

From now on, you will do your work for each lab or homework in a separate directory (or else things will get VERY complicated pretty soon). To get started, create NOW a directory named Lab1 in your class account. In the future, as well as when doing your homework, do this automatically (i.e. create a new directory named Labx or Hwx, where x is the number of the lab or homework, and work in it). Then change your working directory to Lab1.

You do this by using the Unix commands:

mkdir Lab1
cd Lab1

Your first C++ program

Enter your first C++ program with emacs.

At the Unix prompt type
```
		emacs first.cpp
		
```

Enter the following text

		// Program 1
		// simple input/output program.
		// Your name here
		#include <iostream.h>

		main() {
			int apples, students;
			
			cout << "How many apples do you want to share? ";

			cin  >> apples;

			cout << "How many people will share these " 
			     << apples << " apples?" << endl;

			cin  >> students;

			cout << "Each person will get " 
			     << apples/students << " apples" << endl;

		}

Once the program is typed, type ^X^S to save the file. (^X^C would save and terminate the editor, but we want to keep it active.)
Open another window and compile the program:
```
		g++ first.cpp
	
```
Run it (assuming you didn't have any compilation errors).
```
		a.out
	
```

EXERCISE 1: Once your program works, modify it so that it displays also the number of apples left over. For example, if you have 10 apples and 3 students, each student should get 3 apples, and there will be one left over.

Name your source file ex1.cpp.
Skip the second exercise for the time being, and do the Create a typescript and submit part. I want to make sure everybody knows how to create a typescript and that submit works. Then come back and finish the second exercise.

C++: Reading strings of characters

To read a string of characters, use cin.get(string,length,delimiter), where length is the maximum number of characters that can fit in the string, not including the '\0' terminator, and delimiter is the character that marks the end of the input.

Here's an example that reads a string and prints it back.

	char name[20];

	cout << "enter your name: ";
	cin.get(name,19,'\n');
	cin.get();

The second call to cin.get() reads only one character, the end-of-line marker that the first call to cin.get() stopped on, but didn't remove from the input stream.

EXERCISE 2: Write a program that asks the user for her first name, her middle initial, and then her last name, in three different input operations, and then outputs all three of them on the same line, as in this example:
First name?     Marge
Middle Initial? F
Last name?      Philips

Hello Marge F. Philips!
Use two strings and a character to store the three pieces of information. You will have to be careful when you get the middle initial and see if you need to get the end of line (eoln) marker after it or not. You may have to try different options and see which one is the solution.

Creating a typescript and submitting

When you are done with these two exercises, use script to save a copy of the execution.

At the Unix prompt, type script
From this point on, until you type exit, everything that you type in, or that Unix or your programs output to the terminal screen, will automatically go into a file named typescript in the current directory.
You can rename the typescript file, either by giving a different name to start with, by typing
script -o type1
or by using the Unix command mv to rename afterwards, as in:
mv typescript type1
What to do: after you started script, compile and execute one program, then exit. Look into the typescript file with emacs to make sure it looks fine and documents the compilation and execution of your programs. Name it type1 for ex1 and type2 for ex2.
When done, submit the programs and the typescripts by typing:
submit Lab1 filename
where filename is the file you submit (e.g. ex1.cpp or type1).
You are required to submit:
- Two source files ex1.cpp and ex2.cpp
- Two typescript files named type1 and type2 showing the compilation and execution of ex1.cpp and ex2.cpp.
Note: you will have to type submit four times, once for each file you submit.

Wrap Up

Check that you have submitted your work. A first step is to look into the directory where all the files have been copied to. You can do this from your class account with the command:

ls ~112b/handin/Lab1/112b-xx/

where 112b-xx is your hermite account. You will not be able to look inside the directory to see what files are in, but at least you can check that the directory is there.

The ONLY WAY to make sure that you have submitted all the requested files is to have make a list and check each item after you submitted it successfully. If you got an error after submit, your file may not have been submitted, so you'll have to do it again until you got no error.

You can always resubmit (by the deadline). The submit program will ask you if you want to overwrite the old file, so you have a chance to change your mind. As a general strategy from now on, I recommend that you submit the first version that runs satisfactorily (to make sure you do the submission in time), then if you improve it later, resubmit.

Optional: Pipe in input data to your program from a data file

If you are done and want to learn one more trick, then do this part.

Run your first program again, and write down all the keys you pressed to enter input data for it. For example, you might have entered something like:

6 3

or perhaps:

6
3
Create (in emacs) a file named data containing EXACTLY these characters. Check if both formats work (i.e. one line or two lines).
Now run your program again with the input piped in from this file, as follows:
a.out < data
It should work exactly as it did before, when you entered the data directly from the keyboard. If it doesn't, ask me to look at it.
If you did this part, create a third typescript named type3 showing the execution with the data file piped in, and submit it together with the other files.

CS 112b Spring 2004 Ileana Streinu