C99 (previously known as C9X) is an informal name for ISO/IEC 9899:1999, a past version of the C programming language standard.[1] It extends the previous version (C90) with new features for the language and the standard library, and helps implementations make better use of available computer hardware, such as IEEE 754-1985 floating-point arithmetic, and compiler technology.[2] The C11 version of the C programming language standard, published in 2011, replaces C99.