How many versions of the C language are there?

Answer 1

Between 1969 and 1978, C went through several informal revisions with many implementations from a variety of vendors, including Dennis Ritchie himself, the original author of C. During that period the language was not standardised, so vendors added their own extensions which made it difficult to write portable code.

Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language in 1978 and this served as an informal standard for C, which became known as K&R C after the authors.

The American National Standards Institute (ANSI) began standardising the language in 1983 which led to the first formal standard, ANSI X3.159-1989 "Programming Language C", informally known as ANSI C, Standard C or C89. The non-portable UNIX C library was handed off to the IEEE working group 1003 which produced the first POSIX standard in 1988.

In 1990, the ISO/IEC JTC1/SC22/WG14 working group for the International Organisation for Standardisation (ISO) adopted ANSI C as ISO/IEC 9899:1990, informally known as C90. Note that C89 and C90 are essentially the same language, the only real difference being some formatting changes.

In 1995, ISO published a revised standard, ISO/IEC 9899/AMD1:1995, informally known as C95, which incorporated Normative Amendement 1 to the C90 standard.

In 1999, ISO revised the standard again with ISO/IEC 9899:1999, informally known as C99.

In 2008, ISO published a Technical Report addressing the use of nonstandard extensions required in embedded C Programming.

The current C standard is ISO/IEC 9899:2011, informally known as C11.

Today, most implementers support the C99 standard which is largely compatible with C89. However Microsoft predominantly supports the C89 standard along with those parts of C99 required for compatibility with C++.

Answer 2

You might have misunderstood somethings, C language doesn't have "versions".