The C programming language was originally designed for and implemented on the UNIX operating system in 1972 by Dennis Ritchie at bell laboratories of AT&T.  C evolved from two previous programming languages BCPL and B.  Although, C was widely used to develop the UNIX operating system, nowadays also almost all major operating systems are written in C and C++.  In 1983 a committee was established to create an ANSI (American National Standards Institute) standard that would define the C language and this was finally implemented in 1989.  The resulting standard was typically referred to as ANSI/ISO Standard C.  During the 1990s, a new standard for C was developed and is usually referred to as C99. C89 is, however, the version of C in widest use enjoying the greater compiler compatibility and producing the most portable code. It also forms the basis for C++

Some free C compilers

Visual studio community edition>
NetBeans IDE>
Eclipse IDE>
Dev C++
Code Blocks