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Posted 12 Oct 2011
Licenced CPOL

Calculate the Factorial of an Integer in C#

, 19 Oct 2011
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My preference for run-time speed is:long Factorial(int input){ if (input 1; input--) { if (long.MaxValue - answer < answer) throw new...

My preference for run-time speed is:

long Factorial(int input)
    if (input < 0)
        return -1;
    if (input < 2)
        return 1;
    long answer = input;
    for( ;input >1; input--)
        if (long.MaxValue - answer < answer)
            throw new ArithmeticException();
        answer = input * answer;

    return answer;


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Software Developer State of Arkansas & Zycron
United States United States
Bryan Lee learned to code on a RadioShack Color computer II.

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Comments and Discussions

GeneralActually, this is not a joke. How can you check that a multi... Pin
YvesDaoust24-Oct-11 21:51
memberYvesDaoust24-Oct-11 21:51 
GeneralJust for the sake of being picky, how can you be sure that w... Pin
YvesDaoust24-Oct-11 21:45
memberYvesDaoust24-Oct-11 21:45 
GeneralUpdated with simplistic overflow detection. This works only... Pin
USABebopKid19-Oct-11 4:16
memberUSABebopKid19-Oct-11 4:16 
GeneralJust demonstrating my preferred algorithm. And if long is 6... Pin
USABebopKid19-Oct-11 3:21
memberUSABebopKid19-Oct-11 3:21 
GeneralShouldn't you add overflow detection ? (Doing it without the... Pin
YvesDaoust18-Oct-11 22:31
memberYvesDaoust18-Oct-11 22:31 
GeneralTrue, but I do not consider that a means of calculating Fact... Pin
USABebopKid18-Oct-11 4:21
memberUSABebopKid18-Oct-11 4:21 
GeneralAs regards speed, nothing beats Alternative 4. Pin
YvesDaoust17-Oct-11 20:34
memberYvesDaoust17-Oct-11 20:34 

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