Exercise 2: using make
======================

You are going to use *make* to automate the building of your hello world
program.

Create your Makefile
--------------------

Using your favourite editor, create a file called Makefile
(note the capital 'M', which is normal practice here)

------

    hello: hello.c
            gcc -Wall -o hello hello.c

------

There is one critical aspect here: the space at the front of the second line
must be a single TAB. Do not use normal spaces. This is the most common
error made with makefiles.

The rule you have written says:

*    This is a rule to build *hello* (the target)
*    This target depends on *hello.c*; that is, if hello.c changes,
     then hello needs to be rebuilt
*    It gives the command needed to rebuild hello from hello.c

Now you can use it to rebuild your program - but it won't be rebuilt unless
it is necessary to do so. You can force it to be rebuilt using 'touch':
this resets the last-modified time on a file, so that it looks like you've
edited it.

    $ make
    'hello' is up to date
    $ touch hello.c
    $ make
    gcc -Wall -o hello hello.c

Make a change and rebuild
-------------------------

Edit hello.c and make a change to your program. For example, you can change
the string which it prints from *Hello, world!* to something else.

Now rebuild it using make:

    $ make
    gcc -Wall -o hello hello.c
    $ ./hello
    Your new message

Notice how using 'make' makes life easier for the programmer, by issuing the
correct command to recompile the program.