C is an extremely small language. Many of the functions of other languages are not included in C. e.g. No built in I/O, string handling or mathematical functions.
What use is C then?
C provides functionality through a rich set of function libraries.
As a result most C implementations include standard libraries
of functions for many facilities ( I/O etc.). For many practical
purposes these may be regarded as being part of C. But they may vary from
machine to machine. (cf TurboC to UNIX). Appendix 
gives further details on the standard libraries of C.
A programmer can also develop his/ her own function libraries and also include special purpose libraries (e.g. NAG, PHIGS).