Kotlin Program:

Example:

import java.util.Scanner
fun main(args: Array<String>) {

  Scanner userInput = Scanner(System.`in`)
  print("Enter your last number : ")
  var num:Int = userInput.nextInt()
  var fact:Long = 1

  for (i in 1..num)
    fact*=i

  System.out.print("Factorial of $num : $fact")
}

Output:

  Enter your number : 3
  Factorial of 3 : 6

Program

You should know first :

Factorial of N : 1*2*3*4.....*N
Factorial of 0 : 1

The variable which holds factorial value (above fact) must be of type long

Because,
long : Factorial of a number can be very large [ valid for upto 20! ]

for (i in 1..num)
  fact*=i

For greater than 20! , you have to use BigInteger of java Math library

Must import java.math.BigInteger in this case

for (i in 1..num.toLong())
  fact = fact.multiply(BigInteger.valueOf(i);

Concept

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