Introduction to C++

Jonah Warren
jonah AT parsons DOT edu
http://www.feedtank.com/2005/cpp

Lab 1

In this lab, we will go over how to do the following.

Login to the 'A' server and use basic UNIX commands.
Create and edit a file from UNIX using the text editor 'nano' or 'emacs.'
Write a simple program that will print to the screen.
Compile your program using the g++ compiler.
Run your program.
Zip a number of files together, encrypting it, and posting it on the web.

Moving around on the 'A' server.

Using a ssh program (putty, secure ssh, terminal) login to a.parsons.edu using your ftp username and password.
You should see a prompt and cursor that should look like the following:

[name@a name]

This is a unix prompt.

Read this page on the UNIX commands you need to know.

List the files in your current directory by typing ls and hitting return.

You will notice a listing of the files on your web account.
Create a new directory to work in. e.g. mkdir cprog
Type ls. You should see the name of the directory you just created.
Change directories to the one you just created. e.g. cd cprog

You will notice that the command line has change to reflect your current directory.
```
[name@a name cprog]
```

Using nano (or emacs) to create a new file.

Now we want write our first C++ program. We are going to use a UNIX text editor called nano to do this.
(I actually prefer emacs, though nano is a bit simpler. Learn emacs here.)
Type nano HelloWorld.cpp and press return to create a new file.
This will open up the nano text editor.

Type in the following line of code

// HelloWorld.cpp. My first C++ program.

This code will not do anything. When you write //, it means that C++ will ignore the text you write on that line.
Type CTL-X to exit nano. It will ask you if you want to save your changes, say 'yes.' It will ask you what you want to name your file. Type return.
Type ls. You should see the HelloWorld.cpp, the file we just created.

Writing your first C++ program.

Reopen the file we just created by typing nano HelloWorld.cpp.
Type in the following code after the comment we wrote.

// HelloWorld.cpp. My first C++ program.
#include <iostream>
using namespace std;

int main() {
  cout << "HelloWorld in C++.\n";
  return 0;
}

Mysterious huh? We'll get to this later.
Type CTL-X to exit nano. Save your file.

Compiling your first C++ program.

To compile our program we are going to use the g++ compiler. Reference on g++ and gcc (the C compiler) here.
To compile your programs, use the following format g++ filename.cpp -o filename
Thus, to compile the code we just wrote, type the following command:

g++ HelloWorld.cpp -o HelloWorld

This will create an executable file called HelloWorld.
If you have compiler errors, it will print them out now. Read them carefully. They are very helpful. If you see nothing but another prompt, you win! You've compiled your program successfully.

Running your first C++ program.

Running the program once its compiled is easy. Use the following format ./ filename
Thus, to compile the code we just wrote, type the following command:

./HelloWorld

This should run your program. You should see:

HelloWorld in C++.

Preparing to post your files. Zipping and encrypting.

To zip and encrypt your files use the zip command in UNIX. Use the following format zip -e destfile filename1 filename2...
Thus, to zip the HelloWorld.cpp file just wrote and its executable file, type the following command:

zip -e lab_01 HelloWorld.cpp HelloWorld

It will ask you a password, type in a class password, and confirm it.
This will create a file called lab_01.zip.
You may move this file int your web directory with the UNIX cp command ( see UNIX command page) or your favorite FTP program.