This document discusses input and output functions in C language. It describes that input/output functions are part of the standard input/output library provided with C compilers. There are two main types of I/O functions - formatted and unformatted. Formatted functions like scanf() and printf() are used for formatted input and output while unformatted functions like getchar(), putchar(), gets(), puts(), getch(), and getche() are used for non-formatted single character and string input/output. Specific functions and their usage are described in detail.