Programming

Yes.

Code:

#include <stdio.h>

//char* fun(int);

int main()
{
  fun(10);
  return 0;
}

char* fun(int a) {
  return "";
}

Upon compilation,
implicit declaration of ' int ' would be considered for the function fun ' fun ' while the definition is returning ' char* '

IMHO, signatures are a must.

No, that is not true. Function definitions are what would be required in the cases you cite. Function prototypes did not arrive until Ansi C. You have the two mixed up.

function definition: int handler();
function prototype: int handler(int);

The original C language did not support prototypes and, while they are a good idea, they are not required now.

so what will the following do?

Code:

main()
{
long l=get_number();

      printf("%ld\n",l);

      return 0;
}

double get_number()
{
     return 3.141592654;
}

I guess it demonstrates that you are able to generate an incorrect program that doesn't use function prototypes. This suggests that you think this is proof that function prototypes are required and possibly even that the original K&R C supported or required function prototypes. It must at least be true that you think the addition of a function prototype is the only way to fix the program. (I remain convinced that a function definition would fix it as well.) Oh well, at least you finally contributed some code to this thread.

A quote for anyone who is interested...

From The C Programming Language Second Edition by Brian Kernighan and Dennis Ritchie

porter, you and I will simply have to agree to disagree on whether or not function prototypes are currently required as well as whether or not function prototypes were supported (or required) by the original K&R C. I am closing this thread.