Function Call, Arithmetic Operations, User Input and more in Kotlin, Kotlin

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/* 
PROGRAM BY 'JAMES COLLINS'

This program demonstrates the following:
   i - Variable declaration in Kotlin
  ii - User-input in Kotlin using Java's Scanner class.
 iii - Object creation.
  iv - Output.
   v - String formatting.
  vi - Class creation.
 vii - Method declaration.
viii - Passing values to functions/methods.
  ix - Conditional statements
   x - Recursion.
  xi - Comments (Single-line and Mulitline)
    
Thanks for reading.
*/
import java.util.Scanner

class Arithmetic
{
  public fun add(num1: Int, num2: Int): Int
  {
    return num1 + num2 // adding the 2 numbers
  }

public fun diff(num1: Int, num2: Int): Int
  {
    return abs(num1 - num2) // substracting the 2 numbers and getting the absolute value.
  }

public fun multi(num1: Int, num2: Int): Long
  {
    return (num1 * 1L) * num2 // Multiplying 2 numbers.
  }

public fun div(num1: Int, num2: Int): Float
  {
    return (num1 / (num2 * 1.0f)) // Converting one of the numbers to a float so that we can do floating-point calculations.
  }

public fun abs(num:Int): Int
  {
    // This part uses the 'ternary' operator of Kotlin, which is more like an 'if' statement than a simple ternary operator like in Java.
    // In Java you can do this statement like this:- (num < 0) ? -num : num;
    // It easier to type, but I gotta admit, Kotlin's ternary operator is easier to understand from a beginner's perspective.
    return if(num < 0) -num else num 
  }

public fun factorial(num:Int): Long
  {
    if(num == 0)
      return 1
    else if(num == 1)
      return 1
    else
      return num * factorial(num - 1) // This is where the recursion part comes in.
  }
}

fun main() {
  val scanner  = Scanner(System.`in`) // It's good to use 'val' keyword while declaring an Object (Variables declared as 'val' are constants.)
  val practice = Arithmetic()

var num_input: Int = scanner.nextInt() // Variables declared as 'var' are mutable. (value can be changed during runtime.)
  var num_input1: Int = scanner.nextInt()

println("Sum is: ${practice.add(input, input1)}") // Here you can see the way to do string formatting in Kotlin.
  println("Difference is: ${practice.diff(input, input1)}")
  println("Product is: ${practice.multi(input, input1)}")
  println("Quotient is: ${practice.div(input, input1)}")
  println("Facotrial is: ${practice.factorial(5)}")
}

// PROGRAM BY 'JAMES COLLINS'

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