hi,Im learning c from a book written prior to today's ANSI standard and I noticed some things are quite different

1-Must a function which is called in a file before it is defined,be declared with function prototype?

2-Can a Function prototype be declared in each function that calls this particular function,instead of being declared in the beginning of the file?

3-How about function that is defined before it is declared?Is then function prototype not needed?

thank you

The answer to it are
1. the function prototype is required only when it is called before it is defined during the run of the code....
2. yes the function prototype can be declared in each function that calls this particular function, instead of being declared in the beginning of the file...
if it is done so then this declaration would be local to the function... a better practise is to define all the functions at the begining of the file... before the main
3. it is immaterial to declare if the function is defined before it is first called....

hi

But my program works even if I don't use function prototype(assuming function is called prior to its definition)

thank you so much for helping

Just because it works, it doesn't mean it is correct. It may only work with your test case or it could fail on other compilers. The compiler uses the function prototype to determine if the call you are making is of the correct type, etc. If the compiler doesn't know, it guesses. I think it basically assumes that everything in the function call is an int. Depending on what you are doing, that may or may not work.

This is one of those cases where C doesn't do a lot to stop you from shooting yourself in the foot. It is up to the programmer to protect himself by using the prototypes.

certain features if the work may be due to the non compliance with the ansi c.... just use the gcc.... to get better results