How to convert a recursion method into a while loop

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Hi I have this method

Private int recur(int X){
if (X==0)
return 1;
else
return X*recur(X-1);
}

I'm trying to convert to a while loop but it's not working accordingly. taking 5 as a parameter I get different answers.

Private int recur(int x){

C#

int i = 0; int val=0;
       while(i<X){
           if(X==0)
               val= 1;
           else{
               val+= X*(X-1);
               i++;
           }

        }
       return val;

Posted 16-Dec-13 21:21pm

SandraCy

Updated 16-Dec-13 21:45pm

v2

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H.Brydon 17-Dec-13 8:28am

Minor point but when you make the code recursive, I'd suggest "if(x<= 0)" instead of "if(x==0)"...

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OriginalGriff · Answer 1 · 2013-12-16T21:40:00

Solution 1

Um.

Java

Private int recur(int X){
if (X==0)
return 1;
else
return X*(X-1);
}

Isn't recursive...
It always returns X*(X-1), so if you give it "5", it will always return 20, not Factorial(5) or 120...
And your loop version doesn't return a factorial either: The factorial version using a loop would be:

Java

int val = 1;
while (X > 0)
    {
    val *= X--;
    }

Posted 16-Dec-13 21:40pm

OriginalGriff

Comments

SandraCy 17-Dec-13 3:47am

my bad, I made a typing error it's actually "return X* recur(X-1); "

OriginalGriff 17-Dec-13 3:55am

Never type it in - *always* copy and paste!
That way, we get to see what you wrote, rather than what you meant to write - and in my case the two of those can be significantly different! :laugh:

The loop version I showed will work, anyway...