Question

I am trying to do Factorial with Recursion and BigIntegers but eclipse is complaining about the BigInteger. I know the program is supposed to be simple but it is giving me headache. Here is the code.

import java.util.Scanner;
import java.math.BigInteger;

public class Factorial
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter integer");
        BigInteger n = input.nextBigInteger();
        System.out.println("Factorial of " + n + " is "  + fact(n));

    }

    public static  int fact(BigInteger n)
    {
        if(n ==0)
        {
            return 1;
        }
        else
        {
            return n * fact(n-1);
        }
    }
}

Answer 1

BigInteger does not support comparison using == and multiplication using *. Instead, you have to call the appropriate methods of the BigInteger class (equals() and multipy()).

Also note that there exist BigInteger.ZERO and BigInteger.ONE.

Finally, the return type of your fact method should be BigInteger and not int. Whether you want the argument to be of type BigInteger or int is up to you.