[SOLVED] overflow when calculate factorial

[ravinda]

I code a factoial calculating program with self implemented stack. i use long for stack data type. but for values such as 21! it gives a minus value. why is this happening and how to solve it. :confused:

[angryboy]

21! = 51090942171709440000.
what is the max value for long?

You need to use java.math.BigInteger

[pbrockway2]

          21! =  51090942171709440000
Long.MAX_VALUE = 9223372036854775807

why is this happening and how to solve it.

As you yourself say, it's overflowing. Try a more appropriate data type like BigInteger. Or, depending on the accuracy required, an approximation like Stirling's formula.

[Eranga]

A bit more explanation.

I'll just compare this with int and BigInteger. If you are working on with int, after the 12 int produce a garbage. Actually long makes it to 20. Basically throws all the bits out of the range, 32bits for int and 64bits for long. BigInteger also have a limit, which is only on the limit of memory you have.

[ravinda]

I try using BigInteger and it works. It works fine for last numbers like 1000!. thanks for every one who try to help. Specially to Eranga. Thank you.

[Eranga]

It's pleasure to help you lol. :)

So you've solved the problem, please mark the thread solved. You can fin the option on the 'Thread Tools' on top menu of the first post in this thread.

Good luck!

[Eranga]

It's pleasure to help you lol. :)

So you've solved the problem, please mark the thread solved. You can fin the option on the 'Thread Tools' on top menu of the first post in this thread.

Good luck!