Write a Program to find factorial of a number entered by user

import java.util.Scanner;
public class Example1 {

    public static void main(String[] args) {

    //We will find the factorial of this number
        int number;
        System.out.println("Enter the number: ");
        Scanner scanner = new Scanner(System.in);
        number = scanner.nextInt();
        scanner.close();
        long fact = 1;
        int i = 1;
        while(i<=number)
        {
            fact = fact * i;
            i++;
        }
        System.out.println("Factorial of "+number+" is: "+fact);
    }
}

Output:-

Enter the number:

5

Factorial of 5 is: 120

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Example2 :-

Above program does not give correct result for calculating factorial of say 16.

 Because 16! is a large number and can't be stored in integer data type which is of 4 bytes.

To calculate factorial of say hundred we use BigInteger  class of java.math package.

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

class Fact1
{
  public static void main(String args[])
  {
    int n, c;
    BigInteger inc = new BigInteger("1");
    BigInteger fact = new BigInteger("1");

    Scanner input = new Scanner(System.in);

    System.out.println("Input an integer");
    n = input.nextInt();

    for (c = 1; c <= n; c++) {
      fact = fact.multiply(inc);
      inc = inc.add(BigInteger.ONE);
    }

    System.out.println(n + "! = " + fact);
  }
}


Output:-

Input an integer
16
16! = 20922789888000