Control Flow - If Expression

' if ' is an expression is which returns a value. It is used to control the flow of the program structure. There is various type of if expression in Kotlin.

• if-else expression,
• if-else if-else ladder expression,
• nested if the expression

if-else expression

The result of an if-else expression is assigned to a variable.

Note : When using if as an expression, you must also include else (required).

fun main(args: Array<String>) {  
        val num1 = 10  
        val num2 =20  
        val result = if (num1 > num2) {  
            "$num1 is greater than $num2"  
        } else {  
            "$num1 is smaller than $num2"  
        }  
        println(result)  // 10 is smaller than 20
}  

Using if-else expression in one single line statement is like a ternary operator in Java. Kotlin does not support any ternary operator.

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

fun main(args: Array<String>) {  
        val num1 = 10  
        val num2 =20  
        val result = if (num1 > num2) "$num1 is greater than $num2" else "$num1 is smaller than $num2"  
        println(result)  
}  

if-else if-else Ladder Expression

fun main(args: Array<String>) {  
    val num = 10  
    val result = if (num > 0){  
        "$num is positive"  
    }else if(num < 0){  
        "$num is negative"  
    }else{  
        "$num is zero"  
    }  
    println(result) //10 is positive
}  

Nested if Expression

fun main(args: Array<String>) {  
    val num1 = 25  
    val num2 = 20  
    val num3 = 30  
    val result = if (num1 > num2){  
  
        val max = if(num1 > num3){  
            num1  
        }else{  
            num3  
        }  
        "body of if "+max  
    }else if(num2 > num3){  
        "body of else if"+num2  
    }else{  
        "body of else "+num3  
    }  
    println("$result")  // body of if 30
}  

..