A convenient approximation for computing the factorial n! for large valuse of n

Question

A convenient approximation for computing the factorial n! for large valuse of n is given by the Stirling formula n! = (2**n)^(1/2)*(n/e)^n. Where e is the base for natural lograthims, or approximately 2.718282. Write an interger function for computing this approximation to a factorial. Assume the corresponding prototype is int n_fact(int n);

So far I've got;

//

// main.c

// Factorial

//

// Created by Leah Chamberlain on 10/30/15.

// Copyright © 2015 Leah Chamberlain. All rights reserved.

//

#include <stdio.h>

int factorial(int);

double e = 2.718282;

double pi = 3.1415926535;

int main(void){

int n;

printf("enter the number to calculate n! of ");

scanf("%d",&n);

if(n>=1)

printf("n!: %d! is %d ", n,factorial(n));

else

printf("enter an number greater than zero ");

return 0;

}

int n_fact(int n){

int result;

printf("-- %d ",n);

if(n==1)

result = 1;

else

result = pow(n, (n/e)) * sqrt(2*pi*n);

return result;

}

It's not working though

Explanation / Answer

In your program you mention values
double e=2.718282;
double pi=3.1415926535;
but your not mention
#include <math.h>
you didnot return that function.
below is my code

#include <stdio.h>
#include <math.h>

int factorial(int);
int main(){
int i,factorial,num;
printf("enter the number:");
scanf("%d",&num);
factorial=n_fact(num);
printf("Factorial of the %d is: %d",num,factorial);
return 0;
}
int n_fact(int num)
{
int i,f;
for(i=1;i<=num;i++)
f = pow(num, (num/e)) * sqrt(2*pi*num);
return f;
}

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