Compute a factorial.

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:

Code:

---

#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 ^^

Consider using a loop.

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

Code:

---

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.

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.

Quote:

---

Originally Posted by Zlatomir

Code:

---

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?

Code:

---

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