Compute a factorial.

[Miraal]

Heeeello!

I'm trying to find a way how to compute a factorial of any given number.

the factorial of a positive integer is defined as follows:

n! = n(n-1)(n-2)(n-3).....

what I'm trying to do here is to find a way so that the program will know how many steps it need to do to get to (1).

example) I want to compute the factorial of the number 6.

6! = 6(5)(4)(3)(2)(1) = 720

I was just trying something like:

#include <iostream>
using namespace std;

int main()
{
        int n = 0;
	int n1;
	cout << "enter a positive integer and the compute the factorial of: ";
	cin >> n;
	n1 = n(n-1)(n-2)(n-3);
	cout << n1;
	_getch();
	return 0;
}

ofc, this will not work but.. yeah, a little help please ^^

[laserlight]

Consider using a loop.

[TheRogue]

A good place to start would be to have a look at "recursion" for factorial computation.

[Zlatomir]

int factorial (int n)
{	
	int fact = 1;
	for (int i=1; i<=n;i++)
		fact = fact * i;
	return fact;
}

Here is a simple function for calculating factorial, if there is something that you don't understand just ask.

[Lindley]

Be aware, factorials grow fast. 12! will be the largest integer factorial which you can represent in a 32-bit int. Even a 64-bit int can only handle up to 20!. You'll need a BigInt library to handle anything larger.

[Miraal]

int factorial (int n)
{	
	int fact = 1;
	for (int i=1; i<=n;i++)
		fact = fact * i;
	return fact;
}

Here is a simple function for calculating factorial, if there is something that you don't understand just ask.

I tried this and it worked just fine.. but if u please, can you go through it step by step?

[Zlatomir]

int factorial (int n) // function that returns an int value and takes one int parameter
{	
	int fact = 1; 
	for (int i=1; i<=n;i++) {  // this is a for-loop, this execute the code for n times 
                                               // it loops from 1 to n

		fact = fact * i;         // this makes fact equal to fact*i for n times 
        }
	return fact;                     // return value of fact
}

http://www.cplusplus.com/doc/tutorial/control/ Here you have a little tutorial (link is about controlling the execution of a C++ program, the for loop is explained), but i recommend to at least take that tutorial from the beginning.

But it is highly recommended to learn C++ from a book, because in a book the author take you from one topic to another only after he explains the topics you need to understand the new stuff.

Here you have a free book(can be downloaded in pdf or xps format): http://msdn.microsoft.com/en-us/beginner/cc305129.aspx