C language definition

The C programming language definition to consider is ISO/IEC 9899:1990. Older names for this standard are ANSI-C or K&R2 (Kernighan/Ritchie, 2nd Edition 1988 [BK/DR,1988])7.
There is an older standard K&R1 (Kernighan/Ritchie, 1st Edition 1978), also known as pre-ANSI-C.
Use the newer standard if possible. It does rigid type checking (and implicit casting if necessary) on function arguments (provided that function prototypes and appropriate header files are used).
Tools to convert from K&R1 to K&R2 or to add function prototypes are available (e.g. protoize).