* Control Flow

** Conditional expressions

Kotlin provides =if= and =when= for checking conditional expressions

*** When

Use =when= when you have a conditional expressions with multiple branches.
=when= can be used either as a statement or as an expression.

Heres how to use:

+ Place the conditional expression within parentheses =()= and the actions to take within curly braces ={}=
+ Use =->= in each branch to separate each condition from each action

  #+begin_src kotlin
  val obj = "Hello"

  when (obj) {
      "1" -> println("One")
      "Hello" -> println("Greeting")
      else -> println("Unknown")
  }
  #+end_src

#+RESULTS:
: Greeting

Here's an example of using =when= as an expression, the syntax is assigned immediately to a variable:

#+begin_src kotlin
  val result = when (obj) {
      "1" -> "One"
      "Hello" -> "Greeting"
      else -> "Unknown"
  }

  println(result)
#+end_src

#+RESULTS:
: Greeting

If =when= is used as an expression, the else branch is mandatory, unless the compiler can detect
that all possible cases are covered by the branch conditions.

The previous example showed that =when= is useful for matching a variable.
=when= is also useful when you need to check a chain of Boolean expressions

#+begin_src kotlin
  val temp = 18

  val description = when {
      temp < 0 -> "very cold"
      temp < 10 -> "a bit cold"
      temp < 20 -> "warm"
      else -> "hot"
  }

  println(description)
#+end_src

#+RESULTS:
: warm


** Ranges

The most commom way to create a range in Kotlin is to use the =..= operator.
For example, =1..4= is equivalent to =1, 2, 3, 4=.

To declare a range that doesn't include the end value, use the =..<= operator.
For example, =1..<4= is equivalent to =1, 2, 3=.

To declare a range in reverse order, use =downTo=.
For example, =4 downTo 1= is equivalent to =4, 3, 2, 1=.

To declare a range that increments in a step, use =step= and the desired increment value.
For example, =1..5 step 2= is equivalent to =1, 3, 5=.

You can also do the same with =Char= ranges:

+ ='a'..'d'= = ='a', 'b', 'c', 'd'=
+ ='z' downTo 's' step 2= = ='z', 'x', 'v', 't'=