The standard libraries supplied by the C compilation system contain functions that you can use in your program to perform input/output, string handling, and other high-level operations that are not explicitly provided by the C language. Header files contain definitions and declarations that your program will need if it calls a library function. They also contain function-like macros that you can use in your program as you would a function.
In this part, we'll talk a bit more about header files and show you how to use library functions in your program. We'll also describe the contents of some of the more important standard libraries. We'll close with a brief discussion of standard I/O.