How to use BigInteger class?

biginteger, java

Solution

Use `BigInteger` in your `factorial` function, not "after you've done the calculation".

Note also that when multiplying `BigInteger`s, use the `BigInteger.multiply(BigInteger val)` method instead of `*`.

Here's the changed method, which is exactly the same as yours except it uses `BigInteger` instead of `int`:

public static BigInteger factorial(int n){
  int index = n;
  BigInteger total = BigInteger.valueOf(1);
  while(index > 0){
     total = total.multiply(BigInteger.valueOf(index));
     index --;
  }

  return total;
}

Note that also you don't need to convert the return value of the method to a `BigInteger` anymore, e.g. just do:

BigInteger big = factorial(index);

Here's the output:

30: 265252859812191058636308480000000
29: 8841761993739701954543616000000
28: 304888344611713860501504000000
27: 10888869450418352160768000000
26: 403291461126605635584000000
25: 15511210043330985984000000
24: 620448401733239439360000
23: 25852016738884976640000
22: 1124000727777607680000
21: 51090942171709440000
20: 2432902008176640000
19: 121645100408832000
18: 6402373705728000
17: 355687428096000
16: 20922789888000
15: 1307674368000
14: 87178291200
13: 6227020800
12: 479001600
11: 39916800
10: 3628800
9: 362880
8: 40320
7: 5040
6: 720
5: 120
4: 24
3: 6
2: 2
1: 1

Problem

I am having trouble printing numbers past 12!(factorial). Can someone please help me out? I'm not even sure if I'm using this class correctly. ``` public class Application{ public static int factorial(int n){ int index = n; int total = 1; while(index > 0){ total *= index; index --; } return total; } public static void print(int n){ int index = n; while(index > 0){ BigInteger big = BigInteger.valueOf(factorial(index)); System.out.println(index + ": " + big); index --; } } public static void main(String[] args){ int n = 30; print(n); } } ``` and this is a snippet of what it prints out: ``` 18: -898433024 17: -288522240 16: 2004189184 15: 2004310016 14: 1278945280 13: 1932053504 12: 479001600 ```

Original source