.c

Source code for a C or C++ program; may include an entire program's source code, or may be one of may source files referenced within a programming project; can be edited using a basic text editor, but will not show syntax highlighting like most software development programs do.

C++ is the programming language used for creating many of today's software programs. Some Unix compilers use a lowercase ".c" extension for C and an upper case ".C" extension for C++, although this convention is not common.