Editing & Compiling

editing the source code

Unix has at least four different text editors. The most convenient one is emacs. Emacs is extremely powerful, it has nice features like

syntax highlighting,
auto-indentation,
debugging support

which help programming a lot. If you don't know emacs yet, it might be a good idea to learn it. Emacs has a built in tutorial. Experienced users spend most of their time in emacs (even for email, unix shell commands, etc.)

Alternative editors are vi, which takes some time getting used to, and textedit - a very simple editor. The editor pico might be a good choice for people new to unix, it's very similar to the editing mode of the email program pine.

You can start emacs as follows:

log onto your unix account
type emacs followed by return. this is the unix way to start programs. Your command line should look similar to mine:
```
(courses2){biermann}[41]% emacs
```
when the emacs window pops up, select the tutorial from the help menue

compiling and running your program

You should try out one of the example programs, let's say the hello-world program. Here's a step by step explanation of how to compile the program:

type the program (or copy it from the web) and save it as "hello.c". I'm using emacs to enter the program:
```
(courses2){biermann}[43]% emacs hello.c
```
call the compiler from an unix shell - if you're not sure how to do this, just quit your editor and write:
```
(courses2){biermann}[44]% gcc hello.c
```
the compiler is generating an executable with the default name "a.out". Your shell dialogue should look like:
```
(courses2){biermann}[45]% ./a.out
hello, world!
(courses2){biermann}[46]% 
```

some more details

Actually, gcc does multiple steps to create an executable from your source code. At first, your program was compiled into object code, then your code is linked to the libraries in order to create an executable. You can control these these steps separately:

We can compile the source code without actually linking it, using the -c options of the compiler. Gcc is generating a file called "hello.o" for the object code:
```
(courses2){biermann}[56]% gcc -c hello.c
```
In order to link the code, we're just calling gcc with the object file(s) to link. Also, we're providing a name for the executable with the compiler option -o:
```
(courses2){biermann}[57]% gcc hello.o -o hello
```
We can start our program "hello" by typing it's name in the command line. You can also set up your path in such a way, that you don't need to type the beginning "./"
```
(courses2){biermann}[58]% ./hello
hello, world!
(courses2){biermann}[59]%
```

assignment

Try to run at least three of the example programs in class. Use a computer platform, you're familiar with. (Visual C++ should be able to compile the programs under Windows).
Log onto your unix accounts and try the hello-program.
Write a program of your own, use some variables and the input and output commands. You can modify the "circle-area" example.