The answer is
Ondrasej is the "most right" here, IMO.
There are also gui-er ways to do it, without resorting to Xcode. I like TryC.
Mac OS X includes Developer Tools, a developing environment for making Macintosh applications. However, if someone wants to study programming using C, Xcode is too big and too complicated for beginners, to write a small sample program. TryC is very suitable for beginners.
You don't need to launch a huge Xcode application, or type unfamiliar commands in Terminal. Using TryC, you can write, compile and run a C, C++ and Ruby program just like TextEdit. It's only available to compile one source code file but it's enough for trying sample programs.
Just for the record in modern times,
for 2017 !
1 - Just have updated Xcode on your machine as you normally do
2 - Open terminal and
$ xcode-select --install
it will perform a short install of a minute or two.
3 - Launch Xcode. "New" "Project" ... you have to choose "Command line tool"
Note - confusingly this is under the "macOS" tab.
Select "C" language on the next screen...
4- You'll be asked to save the project somewhere on your desktop. The name you give the project here is just the name of the folder that will hold the project. It does not have any importance in the actual software.
5 - You're golden! You can now enjoy c with Mac and Xcode.
Use the gcc compiler. This assumes that you have the developer tools installed.
In 2017, this will do it:
cc myfile.c
You can use gcc, in Terminal, by doing gcc -c tat.c -o tst
however, it doesn't come installed by default. You have to install the XCode package from tour install disc or download from http://developer.apple.com
Here is where to download past developer tools from, which includes XCode 3.1, 3.0, 2.5 ...
http://connect.apple.com/cgi-bin/WebObjects/MemberSite.woa/wo/5.1.17.2.1.3.3.1.0.1.1.0.3.3.3.3.1
You'll need to get a compiler. The easiest way is probably to install XCode development environment from the CDs/DVDs you got with your Mac, which will give you gcc. Then you should be able compile it like
gcc -o mybinaryfile mysourcefile.c
Source: Stackoverflow.com