UNIX supplies a standard package for performing input and output to files or the terminal. This contains most of the functions which will be introduced in this section, along with definitions of the datatypes required to use them. To use these facilities, your program must include these definitions by adding the line This is done by adding the line
#include <stdio.h>near the start of the program file.
If you do not do this, the compiler may complain about undefined functions or datatypes.