Are you using Mavericks? You need to import the library using #include <histedit.h>.

Other problem is that the code won't work with this library. You need to rework it using the following example: http://www.cs.utah.edu/~bigler/code/libedit.html

There's a lot more to set up and tear down when using the Mavericks' editline; it's not so user-friendly for a beginner as the code in the example.