C and C++

Welcome to Dream.In.Code
	Getting C++ Help is Easy! Join 136,055 C++ Programmers for FREE! Get instant access to thousands of C++ experts, tutorials, code snippets, and more! There are 1,623 people online right now. Registration is fast and FREE... Join Now! Chat LIVE With a C++ Expert

help me: factorial with c++!

help me: factorial with c++!, i've been ask to build a program that can perform factorial for a

Options

nhmj88	4 Aug, 2008 - 08:14 AM Post #1
New D.I.C Head Joined: 4 Aug, 2008 Posts: 1	CODE /i've given 2 weeks to solve this problem..i've only have 1 week left! the problems is, i only can get result till factorial 16.. i can get the result for more than that..my lecturer wanted us to solve this problems so we can calculate any large number entered and get the result / #include <iostream> #include <conio.h> using namespace std; int faktorial (int); int main() { cout << faktorial(17); getch(); return 0; } int faktorial (int n) { if (n == 0) return 1; else return n * faktorial (n-1); } This post has been edited by nhmj88: 4 Aug, 2008 - 08:16 AM
	This Post Was Helpful!


Register for Free to Make These Ads Go Away!

KYA	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 08:44 AM Post #2
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,776 Thanked: 91 times Dream Kudos: 1200 My Contributions	Here is some pseudo code for you (actually written in python) python # Factorial function (n!) def factorial(totalElements): n = totalElements f = 1 #0! and 1! = 1 for i in range(2, n+1): f = i return f edited for typo This post has been edited by KYA*: 4 Aug, 2008 - 08:45 AM
	This Post Was Helpful!

KYA

RE: Help Me: Factorial With C++!
4 Aug, 2008 - 08:51 AM

Post #3

#include <nerd.h>

Joined: 14 Sep, 2007
Posts: 4,776

Windows

Thanked: 91 times
Dream Kudos: 1200
My Contributions

Better yet, I wrote this up in C++:

cpp


#include <iostream>
using namespace std;

// Factorial function (n!)
int factorial(int totalElements)
{
    int n = totalElements;
    int f = 1;
    // 0! and 1! = 1
    for (int i = 2; i < n+1; i++)
	{
        f *= i;
	}
    return f;
}

int main()
{
	int total = factorial(3);
	cout << "Total: " << total << endl;
	return 0;
}

Enjoy

This Post Was Helpful!

red_4900	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 08:57 AM Post #4
Code Dreamers Joined: 22 Feb, 2008 Posts: 813 Thanked: 11 times My Contributions	@KYA, edit : ~~if you want to write pseudo code, write it in C or C++. even if it's just a pseudo code. not everyone here can read python code.~~ (damn, that was fast) but from what you do, I guess you're thinking of doing this? cpp cout<<"insert n : "; cin>>n; sum = 1; for(i=1;i<=n;i++) sum = sumi; cout<<endl<<"factorial for "<<n<<" is "<<sum<<endl; but I could only get the factorial up till 12. and nhmj88, your code too can only calculate till factorial of 12. as from from you said, you can calculate up till factorial of 16? but when I checked it with my calculator, it can only gives the correct value until factorial of 12. edit : KYA, your code too can calculate up until factorial of 12 This post has been edited by red_4900*: 4 Aug, 2008 - 09:02 AM
	This Post Was Helpful!

KYA	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 09:02 AM Post #5
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,776 Thanked: 91 times Dream Kudos: 1200 My Contributions	Thats because the variable will roll over. You'll have to make it an unsigned integer. edit: Out of all the languages here, python is one of the easiest to read . This post has been edited by KYA: 4 Aug, 2008 - 09:02 AM
	This Post Was Helpful!

red_4900	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 09:07 AM Post #6
Code Dreamers Joined: 22 Feb, 2008 Posts: 813 Thanked: 11 times My Contributions	I was thinking of the same thing too. but still, I can't get the correct value for factorial larger than 12. this is what I've done : cpp #include<iostream> using namespace std; int main(void){ int i,n; unsigned int sum; cout<<"insert n : "; cin>>n; sum = 1; for(i=1;i<=n;i++) sum = sum*i; cout<<endl<<"factorial for "<<n<<" is "<<sum<<endl; return 0; } ps : I can't read python lol
	This Post Was Helpful!

KYA	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 09:30 AM Post #7
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,776 Thanked: 91 times Dream Kudos: 1200 My Contributions	We could declare a DWORD or higher or have a separate function that divides the number to be factorial ed into sets lower then 12
	This Post Was Helpful!

red_4900	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 09:45 AM Post #8
Code Dreamers Joined: 22 Feb, 2008 Posts: 813 Thanked: 11 times My Contributions	let your code speaks (actually I have no idea what you're talking about )
	This Post Was Helpful!

NickDMax	RE: Help Me: Factorial With C++! 4 Aug, 2008 - 11:01 AM Post #9
2B\|\|!2B Joined: 18 Feb, 2007 Posts: 2,858 Thanked: 49 times Dream Kudos: 550 My Contributions	There is nothing really wrong with the initial code... so whats the problem, well lets see pow(2, 32) = 4294967296; //32 bit unsigned integer's maximum value + 1 pow(2, 64) = 18446744073709551616; //64 bit unsigned integer's max + 1 13! = 6,227,020,800 > 4,294,967,296 -- need something larger than 32 bits. 21! = 51,090,942,171,709,440,000 > 18,446,744,073,709,551,616 -- need more than 64 bits. In general if we use Mathematica to evaluate the following: CODE In[1]:= Fbits[n_]:=N[Floor[Log[2, n!]] + 1] In[2]:= Range[0, 32] //Fbits Out[3]= { 1., 1., 2., 3., 5., 7., 10., 13., 16., 19., 22., 26., 29., 33., 37., 41., 45., 49., 53., 57., 62., 66., 70., 75., 80., 84., 89., 94., 98., 103., 108., 113., 118.} (Sloans A072831)This tells us how many bits n! will require, n=13 requires 34 bits, and n = 32 requires 118 bits (just in case you want to know n=1024 requires 8770 bits or just over 1Kb). i.e. The size of the factorial grows quite fast. You can use the double or long double to hold values past n = 12 (or 20), this actually works quite well since the number of trailing zeros increases so initially the error is actually kept quite small -- but of course the the divergence happens pretty fast as well and before too long the error compounds and the value diverges. So what to do? Well you have to use an arbitrary precision library. or BigInteger library. There are many available on the web. This post has been edited by NickDMax: 4 Aug, 2008 - 11:22 AM
	This Post Was Helpful!