Factorial Java Program

Question

I want to do a factorial program in java using a for loop. For example I want to take the user input, lets say 10, and then multiply 10*9*8*7*6*5*4*3*2*1. I need help constructing the for loop. The code below is all I have so far as I'm not sure where to go after.

import java.util.Scanner;
import java.lang.Math;
public class factorial {

    public static void main(String[] args) {
        int num;
        Scanner input = new Scanner(System.in);
        System.out.println("Enter a number: ");
        num = input.nextInt();
    }
}

Answer 1

Try

public static void main(String[] args) {
    int num;
    int fact=1;
    Scanner input = new Scanner(System.in);
    System.out.println("Enter a number: ");
    num = input.nextInt();
    for (int i=2;i<=num; i++){
        fact=fact*i;
    }

    System.out.println("Factorial: "+fact);
}

As @Marko Topolnik mentioned in comments this code will work for inputs up to 12. For larger inputs will output infinity due to overflow.

For numbers larger than 12 you should use higher data type like BigInteger

You can try:

public static void main(String[] args) {
    BigInteger num;
    BigInteger fact = BigInteger.valueOf(1);
    Scanner input = new Scanner(System.in);
    System.out.println("Enter a number: ");
    num = input.nextBigInteger();
    for (int i = 2; i <= num; i++){
        fact = fact.multiply(BigInteger.valueOf(i));
    }
    System.out.println(fact);
}

Answer 2

Coding by Recursive function:

import java.util.Scanner;

public class Main {

     public static void main(String[] args)
     {
         System.out.print("Enter a number: ");
         Scanner input = new Scanner(System.in);
         int num = input.nextInt();
         long factorialResult = factorialRecursive(num);
         System.out.println(factorialResult);
     }


     public static long factorialRecursive(int n) {
         if (n == 0 || n == 1 )
             return 1;

         return n * factorialRecursive(n - 1);
     }
}

source: learn.uncox.com

If the number is large, "stackoverflow" happens.

Answer 3

Why bother computing it?

public int factorial ( int n ) {
switch(n){
case 0: return 1;
case 1: return 1;
case 2: return 2;
case 3: return 6;
case 4: return 24;
case 5: return 120;
case 6: return 720;
case 7: return 5040;
case 8: return 40320;
case 9: return 362880;
case 10: return 3628800;
case 11: return 39916800;
case 12: return 479001600;
default : throw new IllegalArgumentException();
}

Source : @Emory

Answer 4

This is My Program

class FactorialUsingFor
{
    public static void main(String arg[])
    {
        int factorial = 1;
        int number = 6;

        for(int i = 1; i <= number; i++)
        {
            factorial *= i;
        }

        System.out.println("Factorial of number " + number + " is " + factorial);

    }
}

Answer 5

int sum = 1;

for (int i = 2;i <= num;i++) {
    sum = sum * i;
}

Answer 6

Try this program:=

import java.util.*;
public class Factorials {
 public static void main(String[] args){
  Scanner sc=new Scanner(System.in);
  int i,num,a,b;
  int c=1;
  System.out.println("Enter the no.= ");
  num=sc.nextInt();
  for(i=1;i<=num;i++){
   c=i*c;
  }
  System.out.println("Factorial is "+c);
 }
}