Compilation error in simple function

[livin]

Hi,
I wrote this small code for a factorial of a number in double format. The compiler complains error at fact declaration saying "conflicting types for fact". Where am i going wrong?

#include <stdio.h>
#include <stdlib.h>

int main(){
int i = 0;
double m = 0;
printf("Enter a number whose factorial is needed ");
scanf ("%d", &i);
m = fact(i);
printf("%lf\n", m);
return 0;
}

double fact(int i){

double j = 1;

if (i < 0){
	printf("Invalid Number. Program Exiting now!!\n");
	exit (1);
	}

else
	for(; i > 0 ;){
	j = j * i;
	i--;
        } 
		
return j;
}

[quzah]

#include <stdio.h>
#include <stdlib.h>

int main(){
int i = 0;
double m = 0;
printf("Enter a number whose factorial is needed ");
scanf ("%d", &i);
m = fact(i);
printf("%lf\n", m);
return 0;
}

double fact(int i){

You use fact before you define the function, and you don't have a prototype for it. So since it knows nothing about the function, it assumes it returns an int (and I believe in this case, takes an int). Your program only knows what is above the current line. So the first time it sees fact it looks above and says "I have never seen this. I will assume it is X."

Then it runs into it the second time when you declare the function and says "This isn't what I assumed it to be. You have a problem."


Quzah.

[livin]

Thanks a lot..that was indeed something I didn't know. So it means if u want to define ur function after ur main(), atleast declare a prototype before main(). Else define the function itself before main(). Is what I observed correct?

[CommonTater]

Yep... arrange your functions above main() so that no function is called before it's catalogued... I tend to use prototyping very sparingly.

In C function prototypes allow you to defeat the "functional heirarchy" of the program and often subtle bugs can be introduced by it. In Pascal (where I learned programming) you couldn't do that and, to this day, I still believe it produces better code.

[laserlight]

In C function prototypes allow you to defeat the "functional heirarchy" of the program and often subtle bugs can be introduced by it.

What subtle bugs have you encountered that were introduced by the use of this commonly used feature?

Function prototypes are commonly used because they are what goes in the headers of a library, where functions are concerned.

[CommonTater]

What subtle bugs have you encountered that were introduced by the use of this commonly used feature?

Function prototypes are commonly used because they are what goes in the headers of a library, where functions are concerned.

We've had this conversation before Lase...
And I seem to recall that despite offering you explicit examples, it went noplace.

I guess it comes down to this... Unless you've programmed in a language with rigid structure you won't appreciate the benefits of a functional heirarchy... just like you won't appreciate the benefits of real strings, as opposed to C strings, until you've worked with them. (Sigh... I really miss Pascal...)