Call a function without argument, although it needs one [K&R-C]

Question

It\'s K&R-C and here is the code: http://v6shell.org/history/if.c

Look at the main-Method. There is this line \"if(exp())\".

But the function exp is decl

Answer 1

This is because in c

The compiler will not be able to perform compile-time checking of argument types and arity when the function is applied to some arguments. This can cause problems

Calling an undeclared function is poor style in C (See this) and illegal in C++

for example-

#include

void f(int x); 

int main()
{
   f(); /* Poor style in C, invalid in C++*/
   getchar();
   return 0;
}

void f(int x)
{ 
   printf("%d", x);
}

This program will work but shouldn't be used.See this Wiki link for more.