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The C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system.
C is the most widely used computer language.
This tutorial should be your starting point only.
You can practice C online using compileonline.com
At Tutorials Point you will find references on all important built-in C library functions.
C Built-in Library Function References
A collection of C Programming Sites is given at this page.
C Useful Resources