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 maths functions.
What use is C then?
C provides functionality through a rich set 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 or her own function libraries and also include special purpose libraries (e.g. NAG, PHIGS).