• The developers write several standard Input/Output functions and put them in libraries. These libraries are available with all C compilers. Whichever C compiler you are using it’s almost certain that you have access to a library of I/O functions. 

  • The way one Operating System displays output on screen can be different from the way of other Operating Systems.

  • There are numerous library functions available for I/O.

  • These can be classified into two broad categories: 

  1. Console I/O functions- Functions to receive input from keyboard and write output to VDU.

  2. File I/O functions- Functions to perform I/O operations on a floppy disk or hard disk.