Using header files for declarations and source files for definitions

The two types of files we will use to group functions are header files and source code files – or, more simply, just source files. Nearly all of the programs we have created thus far have been single-file source files that have included struct and enum definitions, typedef keywords, function prototypes, and functions. This is not typical in C programming; we have only been doing this to keep our programs more condensed. It is far more typical for C programs to consist of the main source file – where the main() function is defined – and one or more header files and auxiliary source files. The sortNames().c, nameList.h, and nameList.c programs are typical examples of common C programs.

Whenever the preprocessor sees the #include directive, which must be followed by a filename, it opens that file and reads it into the input stream for compilation at that location, just as if...