How to Write a function factorial

[cemtkr]

The question is "Write a function factorial, which calculates the factorial of an integer. "
so how can i write this function
please aid me!

[D80DSL3A]

Try searching this site for "factorial function" or similar.
The problem has appeared countless times on this site.

[ascii]

this is the classic example of a program where recursion is the most efficient way to calculate it. also im pretty sure C++ starts to be incorrect starting at around 15! or so.

hint: the base case is when you have to multiply by 1 :)

[buffbill]

Can you define mathematically say 9!

[Janlan]

#include <iostream>
using namespace std;

int factorial (int x);

int main () 
{

	int n;
		cout<<"Enter number: ";
		cin>>n;

		int fact;

		fact = factorial(n);

		cout<<"The factorial of number: "<<n<<" is: "<<fact<<endl;

		cin.get(); cin.get();
		return 0;
}

int factorial(int x)
{

int i;
int F=1;

for (i = 1; i <= x; i++)
	F*=i;

	return F;
}

[savavampir]

@ascii

...C++ starts to be incorrect starting at around 15.

That is wrong statement. Its not C++ that is incorrect, you must use type that can accept/hold large numbers. See (for example) this: http://www.cplusplus.com/reference/std/limits/numeric_limits/
Make your own type that can represent these numbers or use some library for this purpose.

[ascii]

:o thank you thats an interesting class :)

[mcqueen]

Here is a factorial code.

#include <cstdlib>
#include <iostream>

using namespace std;

int factorial(int x)
{
   int y=1 ;
   int z=x ;
   int fact ;
   for (x=x-1; x>0; x--)
   {
      y=y*x ;
   }
   fact=y*z ;
   return fact ;
}
int main()
{
   int n ;
   cout<<"Enter a number: " ;
   cin>> n ;
   cout<<n <<"!=" <<factorial(n) <<endl ;
   system("PAUSE") ;
}

[Janlan]

Why so complicated? :)

[mcqueen]

Thats not complicated, its short simple and to the point.

[ascii]

as i pointed out before this excersise is best down with a recursive function

#include <iostream>
using std::cout;
using std::endl;
using std::cin;

int factorial(int number)
{
	int fact = number;
	if (number == 1)
		return 1;
	else
		return fact * factorial(number - 1);
}

int main(void)
{
	int number;
	cout << "Enter a number: " << endl;
	cin >> number;
	cout << factorial(number);

	cout << endl;
	return 0;
}

this is far more efficient :)

also doesnt use system commands :o

[mcqueen]

recursive function is better. Sorry i forgot about it

[buffbill]

@mcqueen ...no it's not. Try getting the value of 51! or even 27!

[ascii]

whats your point buffbill? a recursive function is the most efficient. factorial 27 is probably out of the range of an int anyways, and 51 certainly is.

[cnoeval]

Using recursion is the standard way but since you've done the OP's homework for him and he's probably gone, what's the point of the debate???

[ascii]

debating the most effective method?

[savavampir]

typedef unsigned long int ulong;
ulong factorial(ulong num)
{
	if (1 >= num)
		return 1;
	return num * factorial(num - 1);
}

even this is better for big numbers up to 65:

typedef unsigned long long int ulong;

[ascii]

good idea :)

[webJose]

Ok, this is it:

typedef whatever_you_want fact_type;
fact_type factorial(fact_type n) //I HATE camel casing for functions.  How come you guys like it so much???
{
    if (n == 0) return 1;
    if (n < 3) return n;
    return n * factorial(n -1);
}