How to write algorithm to workout factorial recursion in C#?

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Hi Team

I need some help as to write factorial recursion in c#, below is my thought around writing this in c# the algorithm.

What I have tried:

C#

// C# program to find factorial 
// of given number 
using System; 

class Test { 
	// method to find factorial 
	// of given number 
	static int factorial(int n) 
	{ 
		if (n == 0) 
			return 1; 

		return n * factorial(n - 1); 
	} 

	// Driver method 
	public static void Main() 
	{ 
		int num = 5; 
		Console.WriteLine("Factorial of "
						+ num + " is " + factorial(5)); 
	} 
}

Posted 11-Nov-20 9:49am

gcogco10

Updated 11-Nov-20 10:46am

CPallini

v2

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Comments

Richard MacCutchan 11-Nov-20 15:57pm

What is wrong with that?

CPallini 11-Nov-20 16:01pm

Your code is fine. What's the problem then?

gcogco10 11-Nov-20 16:30pm

Yes the code is fine, what i want to know. This program uses algorithm to work on recursion yes or no? If not how will improve this code?

Dave Kreskowiak 11-Nov-20 17:12pm

Answering the question of recursion is simple. Does the function doing the work call itself? If it does, then the answer is Yes.

You might want to look at your factorial function code to answer that.

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OriginalGriff · Accepted Answer · 2020-11-11T10:47:00

Solution 1

Quote:
This program uses algorithm to work on recursion yes or no? If not how will improve this code?

Yes. Sort of. It only ever returns 120, regardless of the value I put in num

Factorial of 3 is 120

To improve it? Don't calculate it at all. Instead, precalculate all the ones which fit in a 32 bit integer. Since there are only 13 of them (0! to 12! inclusive) it's simpler, quicker, and a lot more memory efficient to allocate an array of 13 integers, and just check that the requested value is in range. Your app either crashes or gives the wrong value if I request 13! or above ...

Posted 11-Nov-20 10:47am

OriginalGriff

Comments

Richard MacCutchan 12-Nov-20 5:23am

Console.WriteLine("Factorial of " + num + " is " + factorial(5));

OriginalGriff 12-Nov-20 6:06am

I kinda noticed that ... but he didn't.
Nice simple little bit of debugging for him (and an indication of his testing regimen :sigh: )

Richard MacCutchan 12-Nov-20 6:18am

Apologies, I should have known that.

OriginalGriff 12-Nov-20 6:22am

No need to apologise! :D