It's interesting to know how this code is working...?

Question

#include <stdio.h>
//int rec(int x);// to remove warning please un-comment this
int main()
{
int a=5,fact;
fact=rec(a);
printf ("Factorial value = %d", fact);
return 0;
}

int rec(x) //how this line is working?
int x;
{
int f;
if(x == 1)
return (1);
else
f=x*rec (x-1);
return (f);
}

https://code.sololearn.com/cTG4wwyR4aBh/?ref=app
https://code.sololearn.com/cTG4wwyR4aBh/?ref=app

Answer 1

The syntax is an ancient way of declaring a function.

int rec(x)
int x;
{
...
}

is equivalent to

int rec(int x)
{
...
}

Answer 2

Definition of function "rec()" should write before main() function, if You don't want to write function Prototype [ i.e. int rec(int x); ].
And Run It.
Then You will get Output without Warnings.