Kotlin if…else expressions works like an if…else expression in any other Modern Computer Programming. So let”s start with our traditional if…else statement available in Kotlin.

Syntax

The syntax of a traditional if…else expression is as follows:

if (condition) {
   // code block A to be executed if condition is true
} else {
  // code block B to be executed if condition is false
}

Here if statement is executed and the given condition is checked. If this condition is evaluated to true then code block A is executed, otherwise program goes into else part and code block B is executed.

Example

You can try the following example:

fun main(args: Array<String>) {
    val age:Int = 10

    if (age > 18) {
        print("Adult")
    } else {
        print("Minor")
    }
}

When you run the above Kotlin program, it will generate the following output:

Minor

Kotlin if…else Expression

Kotlin if…else can also be used as an expression which returns a value and this value can be assigned to a variable. Below is a simple syntax of Kotlin if…else expression:

Syntax

val result = if (condition) {
   // code block A to be executed if condition is true
} else {
  // code block B to be executed if condition is false
}

If you”re using if as an expression, for example, for returning its value or assigning it to a variable, the else branch is mandatory.

Examples

fun main(args: Array<String>) {
    val age:Int = 10

    val result = if (age > 18) {
        "Adult"
    } else {
        "Minor"
    }
    println(result)
}

When you run the above Kotlin program, it will generate the following output:

Minor

You can ommit the curly braces {} when if has only one statement:

fun main(args: Array<String>) {
    val age:Int = 10

    val result = if (age > 18) "Adult" else  "Minor"
    println(result)
}

When you run the above Kotlin program, it will generate the following output:

Minor

You can include multiple statements in if…else block, in this case the last expression is returned as the value of the block. Try the following example:

fun main(args: Array<String>) {
    val age:Int = 10

    val result = if (age > 18) {
        println("Given condition is true")
        "Adult"
    } else {
        println("Given condition is false")
        "Minor"
    }
    print("The value of result : ")
    println(result)
}

When you run the above Kotlin program, it will generate the following output:

Given condition is false
The value of result : Minor

Kotlin if…else…if Ladder

You can use else if condition to specify a new condition if the first condition is false.

Syntax

if (condition1) {
  // code block A to be executed if condition1 is true
} else if (condition2) {
  // code block B to be executed if condition2 is true
} else {
  // code block C to be executed if condition1 and condition2 are false
}

Example

fun main(args: Array<String>) {
    val age:Int = 13

    val result = if (age > 19) {
        "Adult"
    } else if ( age > 12 && age  < 20 ){
        "Teen"
    } else {
        "Minor"
    }
    print("The value of result : ")
    println(result)
}

When you run the above Kotlin program, it will generate the following output:

The value of result : Teen

Kotlin Nested if Expression

Kotlin allows to put an if expression inside another if expression. This is called nested if expression

Syntax

if(condition1) {
   // code block A to be executed if condition1 is true
   if( (condition2) {
      // code block B to be executed if condition2 is true
   }else{
      // code block C to be executed if condition2 is fals
   }
} else {
  // code block D to be executed if condition1 is false
}

Example

fun main(args: Array<String>) {
    val age:Int = 20 

    val result = if (age > 12) {
       if ( age > 12 && age  < 20 ){
           "Teen"
       }else{
           "Adult"
       }
    } else {
        "Minor"
    }
    print("The value of result : ")
    println(result)
}

When you run the above Kotlin program, it will generate the following output:

The value of result : Adult

fun main(args: Array<String>) {

    var x = 20
    var y = 15
    var z = "Mango"

    val result = if (x > y ) {
       z = "Orange"
    } else {
       z = "Apple"
    }
    println("Value of result = $z")
}