************
Hello, World
************

Just to make sure we have the necessary tools for this course, we'll
do a quick `"Hello, World!"
<https://en.wikipedia.org/wiki/%22Hello,_World!%22_program>`_ program.

This will use a few concepts that we will explore in depth shortly.

To write the code for our program, we need an editor.  We'll use
the simple ``nano`` editor here, but we'll explore others in a
bit.

We start at the Unix command line, indicated by the ``$`` prompt.

Open nano on the command line simply by typing ``nano``:


.. prompt:: bash

   nano

You should have a window that looks something like this:

.. image:: nano.png
   :width: 90%
   :align: center
   :alt: the nano editor

Now we can simply type our C++ code in the window.  Enter the following:

.. code:: c++

   #include <iostream>

   int main() {
      std::cout << "Hello, World!" << std::endl;
      return 0;
   }

Now save it by doing ``^O``, where ``^`` here means you hold down the *control* key on the keyword.

It will ask for a name, so we'll use ``hello.cpp``.

Now we can exit via ``^X``.

We just created the source code for our first program.  We now need to
compile it into instructions the computer understands.  The C++
compiler we will be using is called ``g++`` and we compile this simple
program as:

.. prompt:: bash

   g++ -o hello hello.cpp

Then we can run our program as:

.. prompt:: bash

   ./hello


Next Steps
==========

There is quite a lot going on here that we need to understand before we dive more deeply into C++:

* We started out with a simple ``$`` *prompt* in our terminal.  What else can we do there?

* How does Unix manage files (like ``hello.cpp``) and how can we copy, modify, move, etc. them?

* What is that compiler command doing? what does the ``-o`` mean?

* What is the meaning of the ``./`` that we put in front of ``hello``?

We'll start by learning more about Unix, the Unix filesystem, and how to work with the command line.

After that' we'll move onto programming.