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Index › Programming Questions & Help › Syntax Questions › Problem with bigger factorial values
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Problem with bigger factorial values (Read 864 times)
DA.B
Problem with bigger factorial values
Mar 23rd, 2009, 11:41pm  
Hi forum,
I need to work with bigger factorials.
I already read about the problems with the big numbers.

This code would not work for integers bigger than 19, on a PC.

void draw() {
   int f = fact(20);
   println(f);
}

int fact(int n) {
 if (n <= 1) {
   return 1;
 }
 else {
   return n * fact(n-1);
 }
}


But I've found this link:
http://leepoint.net/notes-java/data/numbers/60factorial.html

I have no idea how to use the java.Math.BigInteger for my sketch - does anyone has an idea?
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PhiLho 
Re: Problem with bigger factorial values
Reply #1 - Mar 24th, 2009, 6:50am  
The page you point to is good, showing that a recursive solution as you use is bad, and providing full code for calculating a factorial iteratively.

You can use the content of the main() function as is in your Processing sketch.
I wouldn't put that in draw(), though, unless you really need to compute that 60 times per second. setup() is a better place.
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DA.B
Re: Problem with bigger factorial values
Reply #2 - Mar 24th, 2009, 9:40am  
Thank you PhiLho.

that was really easy... Still much to learn!

This is the code

import java.math.BigInteger;
void setup(){
 BigInteger n = BigInteger.ONE;
 for (int i=1; i<=20; i++) {
   n = n.multiply(BigInteger.valueOf(i));
   System.out.println(i + "! = " + n);
 }
}
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PhiLho 
Re: Problem with bigger factorial values
Reply #3 - Mar 24th, 2009, 10:33am  
As said in the linked page, factorial is the "Hello World!" of recursive functions because it is so simple... and the worst example, because it is also trivial to do it in iterative fashion. Fibonacci is perhaps a better usage of recursiveness.

Note: Processing has a "native" println, no need for System.out.println.
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