How can I calculate a factorial in C# using a library call?

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I need to calculate the factorial of numbers up to around 100! in order to determine if a series of coin flip-style data is random, as per this Wikipedia entry on Bayesian probability. As you can see there, the necessary formula involves 3 factorial calculations (but, interestingly, two of those factorial calculations are calculated along the way to the third).

I saw this question here, but I'd think that integer is going to get blown out pretty quickly. I could also make a function that is more intelligent about the factorial calculation (ie, if I have 11!/(7!3!), as per the wiki example, I could go to (11*10*9*8)/3!), but that smacks of premature optimization to me, in the sense that I want it to work, but I don't care about speed (yet).

So what's a good C# library I can call to calculate the factorial in order to get that probability? I'm not interested in all the awesomeness that can go into factorial calculation, I just want the result in a way that I can manipulate it. There does not appear to be a factorial function in the Math namespace, hence the question.

You could try Math.NET - I haven't used that library, but they do list Factorial and Logarithmic Factorial.

3 Different ways to calculate factorial in C# – Csharp Star, This C# Program generates Factorial of the Number obtained from the user. 1. Using For Loop:. In this article, we will discuss different ways for calculating factorial in C#. Factorial of a number is obtained from the result of multiplying a series of descending natural numbers. This C# Program generates Factorial of the Number obtained from the user. 1. Using For Loop:

There has been a previous question on a similar topic. Someone there linked the Fast Factorial Functions web site, which includes some explanations of efficient algorithms and even C# source code.

C# Sharp Exercises: Calculate the factorial of a given number , C# Sharp For Loop: Exercise-15 with Solution. Write a C# Sharp program to calculate the factorial of a given number. Pictorial Presentation:. To calculate a factorial in C#, you can use any of the following three ways − Calculate factorial with for loop Example. Live Demo. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace factorial { class Test { static void Main(string[] args) { int i, res; int value = 5; res = value; for (i = value - 1; i >= 1; i--) { res = res * i; } Console

Do you want to calculate factorials, or binomial coefficients?

It sounds like you want to calculate binomial coefficients - especially as you mention 11!/(7!3!).

There may be a library that can do this for you, but as a (presumably) programmer visiting stack overflow there's no reason not to write one yourself. It's not too complicated.

To avoid memory overflow, don't evaluate the result until all common factors are removed.

This algorithm still needs to be improved, but you have the basis for a good algorithm here. The denominator values need to be split into their prime factors for the best result. As it stands, this will run for n = 50 quite quickly.

float CalculateBinomial(int n, int k)
{
    var numerator = new List<int>();
    var denominator = new List<int>();
    var denominatorOld = new List<int>();

    // again ignore the k! common terms
    for (int i = k + 1; i <= n; i++)
        numerator.Add(i);

    for (int i = 1; i <= (n - k); i++)
    {
        denominator.AddRange(SplitIntoPrimeFactors(i));
    }

    // remove all common factors
    int remainder;                
    for (int i = 0; i < numerator.Count(); i++)
    {
        for (int j = 0; j < denominator.Count() 
            && numerator[i] >= denominator[j]; j++)
        {
            if (denominator[j] > 1)
            {
                int result = Math.DivRem(numerator[i], denominator[j], out remainder);
                if (remainder == 0)
                {
                    numerator[i] = result;
                    denominator[j] = 1;
                }
            }
        }
    }

    float denominatorResult = 1;
    float numeratorResult = 1;

    denominator.RemoveAll(x => x == 1);
    numerator.RemoveAll(x => x == 1);

    denominator.ForEach(d => denominatorResult = denominatorResult * d);
    numerator.ForEach(num => numeratorResult = numeratorResult * num);

    return numeratorResult / denominatorResult;
}

static List<int> Primes = new List<int>() { 2, 3, 5, 7, 11, 13, 17, 19, 
    23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 };

List<int> SplitIntoPrimeFactors(int x)
{
    var results = new List<int>();
    int remainder = 0;

    int i = 0;
    while (!Primes.Contains(x) && x != 1)
    {
        int result = Math.DivRem(x, Primes[i], out remainder);
        if (remainder == 0)
        {
            results.Add(Primes[i]);
            x = result;
            i = 0;
        }
        else
        {
            i++;
        }
    }
    results.Add(x);
    return results;
}

I can estimate n = 110, k = 50 (returns 6x10^31) but cannot run n = 120, k = 50.

C# factorial, To calculate factorial in C#, you can use while loop and loop through until the number is not equal to 1.Here n is the value for which you want� Factorial of a number using the do-while loop in C#: In the below program, we use the do-while loop to calculate the factorial of a given number. The number here we are taking from the console.

using System;
//calculating factorial with recursion
namespace ConsoleApplication2
{
    class Program
    {
        long fun(long a)
        {
            if (a <= 1)
            {
                return 1;}
            else
            {
                long c = a * fun(a - 1);
                return c;
            }}

        static void Main(string[] args)
        {

            Console.WriteLine("enter the number");
            long num = Convert.ToInt64(Console.ReadLine());
            Console.WriteLine(new Program().fun(num));
            Console.ReadLine();
        }
    }
}

Write a C# program to calculate a factorial using recursion, Factorial of a number is what we are finding using a recursive function checkFact () in the below example −If Login � Library � Videos � eBooks Write a C# program to calculate a factorial using recursion If not, then the recursive function will be called for the following iterations if you want the value of 5! Calculate the factorial of a given number: -------------------------------------------- Input the number : 6 The Factorial of 6 is: 720.

The following can calculate the factorial of 5000 in 1 second.

public class Number
{
    #region Fields
    private static long _valueDivision = 1000000000;
    private static int _valueDivisionDigitCount = 9;
    private static string _formatZeros = "000000000";
    List<long> _value;
    #endregion

    #region Properties
    public int ValueCount { get { return _value.Count; } }
    public long ValueAsLong
    {
        get
        {
            return long.Parse(ToString());
        }
        set { SetValue(value.ToString()); }
    }
    #endregion

    #region Constructors
    public Number()
    {
        _value = new List<long>();
    }
    public Number(long value)
        : this()
    {
        SetValue(value.ToString());
    }
    public Number(string value)
        : this()
    {
        SetValue(value);
    }
    private Number(List<long> list)
    {
        _value = list;
    }
    #endregion

    #region Public Methods
    public void SetValue(string value)
    {
        _value.Clear();
        bool finished = false;
        while (!finished)
        {
            if (value.Length > _valueDivisionDigitCount)
            {
                _value.Add(long.Parse(value.Substring(value.Length - _valueDivisionDigitCount)));
                value = value.Remove(value.Length - _valueDivisionDigitCount, _valueDivisionDigitCount);
            }
            else
            {
                _value.Add(long.Parse(value));
                finished = true;
            }
        }
    }
    #endregion

    #region Static Methods
    public static Number operator +(Number c1, Number c2)
    {
        return Add(c1, c2);
    }
    public static Number operator *(Number c1, Number c2)
    {
        return Mul(c1, c2);
    }
    private static Number Add(Number value1, Number value2)
    {
        Number result = new Number();
        int count = Math.Max(value1._value.Count, value2._value.Count);
        long reminder = 0;
        long firstValue, secondValue;
        for (int i = 0; i < count; i++)
        {
            firstValue = 0;
            secondValue = 0;
            if (value1._value.Count > i)
            {
                firstValue = value1._value[i];
            }
            if (value2._value.Count > i)
            {
                secondValue = value2._value[i];
            }
            reminder += firstValue + secondValue;
            result._value.Add(reminder % _valueDivision);
            reminder /= _valueDivision;
        }
        while (reminder > 0)
        {
            result._value.Add(reminder % _valueDivision);
            reminder /= _valueDivision;
        }
        return result;
    }
    private static Number Mul(Number value1, Number value2)
    {
        List<List<long>> values = new List<List<long>>();
        for (int i = 0; i < value2._value.Count; i++)
        {
            values.Add(new List<long>());
            long lastremain = 0;
            for (int j = 0; j < value1._value.Count; j++)
            {
                values[i].Add(((value1._value[j] * value2._value[i] + lastremain) % _valueDivision));
                lastremain = ((value1._value[j] * value2._value[i] + lastremain) / _valueDivision);
                //result.Add(();
            }
            while (lastremain > 0)
            {
                values[i].Add((lastremain % _valueDivision));
                lastremain /= _valueDivision;
            }
        }
        List<long> result = new List<long>();
        for (int i = 0; i < values.Count; i++)
        {
            for (int j = 0; j < i; j++)
            {
                values[i].Insert(0, 0);
            }
        }
        int count = values.Select(list => list.Count).Max();
        int index = 0;
        long lastRemain = 0;
        while (count > 0)
        {
            for (int i = 0; i < values.Count; i++)
            {
                if (values[i].Count > index)
                    lastRemain += values[i][index];
            }
            result.Add((lastRemain % _valueDivision));
            lastRemain /= _valueDivision;
            count -= 1;
            index += 1;
        }
        while (lastRemain > 0)
        {
            result.Add((lastRemain % _valueDivision));
            lastRemain /= _valueDivision;
        }
        return new Number(result);
    }
    #endregion

    #region Overriden Methods Of Object
    public override string ToString()
    {
        string result = string.Empty;
        for (int i = 0; i < _value.Count; i++)
        {
            result = _value[i].ToString(_formatZeros) + result;
        }
        return result.TrimStart('0');
    }
    #endregion
}

class Program
{
    static void Main(string[] args)
    {
        Number number1 = new Number(5000);
        DateTime dateTime = DateTime.Now;
        string s = Factorial(number1).ToString();
        TimeSpan timeSpan = DateTime.Now - dateTime;
        long sum = s.Select(c => (long) (c - '0')).Sum();
    }
    static Number Factorial(Number value)
    {
        if( value.ValueCount==1 && value.ValueAsLong==2)
        {
            return value;
        }
        return Factorial(new Number(value.ValueAsLong - 1)) * value;
    }
}

Calculate the Factorial of an Integer in C#, Calculate the Factorial of an Integer in C# It could be done using Recursive Lambda Expression, for example,class Program{ static Func Factorial = x => x < 0 ? -1 : x == 1 || x == 0 ? 1 : x * Factorial(x - 1); static void Main(string[] args) { Console. WriteLine(Factorial(5)); }}(The code Finding the area of a trapezoid in C# with given sides a, b and the height h; How to find the last digit of a number "n" and print it in C#; Calculate Factorial of a number in JavaScript; Calculate the weight of a man on the Moon in C#; How to calculate the perimeter (circumference) of a circle in C#? How to calculate the area of a circle in C#?

One line function for factorial of a number, We can find the factorial of a number in one line with the help of Ternary operator or commonly known as Conditional operator in recursion. Recommended:� Let's solve factorial of number by using recursion. We know that in factorial number value is multiple by its previous number so our problem is divided in small part. using System; namespace FactorialExample { class Program { static void Main(string [] args) { Console.WriteLine("Enter a number");

Factorial Function in Math Library, Hey,I was wondering, does anybody know if c++ has a factorial function = in its math library? This code counts downwards if you start with a negative, and will run out of stack space and crash your application. My Casio calculator holds 100 decimal digits, which is good to 69! Error When Specifying Code in C#. Previous: Write a program in C# Sharp to Check whether a given String is Palindrome or not using recursion. Next: Write a program in C# Sharp to find the Fibonacci numbers for a n numbers of series using recursion.

Math Class (System), several mathematical and trigonometric functions from the Math class to calculate the inner C# Copy. Run. /// <summary> /// The following class represents simple functionality </summary> using System; namespace MathClassCS { class� Factorial is undefined for negative numbers. This code counts downwards if you start with a negative, and will run out of stack space and crash your application. Factorial grows rather fast. In a really old machine, int means a 16-bit signed int, and 7! is the highest which that will hold.

Comments
  • See also the same in Math.NET Numerics, the successor of the linked Math.NET Iridium library.
  • Checking it out now-- man, I really wish there were some best-approximation-may-not-work-for-everyone implementation as part of the base libraries.
  • The problem with that code is that the downloads appear to be all in java, and I'm just not interested in the work to convert from java to C#. The author probably has C# code to download, but the Math.Net solution puts the result into a double, which is exactly what I need.
  • And what happens when n ~= 50 and k ~= 2? Overflow! I need some way to handle nontrivial cases.
  • In that case you calculate n = 50 and k = 48 as I pointed out.
  • ok. What's 48!? Will that fit into an integer? Because that's what your denominator is doing in that case.
  • Regardless of the algorithm, the result of, say, nCr for n = 100 and r = 50 will overflow a 64 bit number. You need to go back to your original problem because you can't store that result.
  • Only if I don't go with an algorithm that uses something like Stirling's Approximation or the like, putting the result into a double. The next step in the algorithm is a rudimentary integration, so 'close enough' will be just fine, and the precision loss on a double is ok.
  • Please read the other answers. This is not a sufficient solution, because long does not have the capacity to handle the size of a number near 100!. As such, some other method (such as Stirling's approximation) need to be used instead.
  • It doesn't do run in 1 second on my computer ;)