In this post, we will learn how to use kotlin if else block. There are 2 ways to use kotlin if else block –
a. Traditional way.
b. As an Expression.

a. Traditional way to use kotlin if else block

You can use if else block as an statement. This is traditional way to use if else block.

Syntax to use kotlin if else block as an statement is

if(testCondiction)
// Code to perform some action when testCondition is true.

or

if(testCondition)
	// Code to perform some action when testCondition is true
else
	// Code to perform some other action when testCondition is false

It means if statement can be followed by optional else statement.

– Example,

fun main(args: Array<String>) {
    var a = 20
    var b = 30
    var max = a
    if (a < b) max = b
    println("max = $max")
}

When the above code is run, you will get below output
max = 30

fun main(args: Array<String>) {
	var a = 20
	var b = 30
	if (a < b) {
		a = a * 2
		println(a)
	}
	else	{
		b = b * 2
		println(b)	
	}

}

When the above code is run, you will get below output
40

Since a is smaller than b, a will be multiplied by 2.

Important points to keep in mind while using kotlin if else block as an statement

a. If block may have zero or more else block conditions. You can also only use if block.
b. If block may have zero or more else if block conditions. i.e. You can only use if block or there may be if else if else….. else block conditions.
c. If any of the if block or else if block conditions succeeds, then, remaining conditions will not be tested.

– Example

fun main(args: Array<String>) {
	var a = 40
	if (a < 10) {
	   println("a is smaller than 10")
	}
	else if(a < 20) {
	   println("a is smaller than 20")
	}
	else if(a < 30) {
	   println("a is smaller than 30")
	}
	else if(a < 40) {
	   println("a is smaller than 40")
	}
	else if(a < 50) {
	   println("a is smaller than 50")
	}
	else if(a < 60) {
	   println("a is smaller than 60")
	}
	else {
	   println("a is greater than or equal to 60")
	}

}

When you run the above program, you will get below output
a is smaller than 50

At fist, a < 10 will be tested. If it fails, then, a < 20, then, a < 30..and so on. Conditions upto a < 50 will be tested. Since a < 50 condition will succeed, remaining test conditions will not be tested.

b. Use Kotlin If Else block As an Expression

Unlike Java or any other programming language, you can also use If else block as an expression in kotlin. It means it returns a value. When you are using if as an expression, you must have else statement.

Syntax to use kotlin if else block as an expression is –

if(condition1) {
	// Code to perform some actions when condition1 is true..
	// Last statement is the value to be returned when condition1 is true…
} else {
	// Code to perform when condition1 is false…
	// Last statement is the value to be returned when condition1 is false…
}

– Example,

fun main(args: Array<String>) {
	var a = 20
	var b = 30
	val max = if (a > b) {
	     a
	}
	 else {
             b
	}
	println("max = $max")
}

When you run the program, you will get below output:
max = 30

NOTE: The curly brackets are optional if there is only one statement to be executed within condition. For example,

Statement 1:

	val max = if (a > b) {
	     a
	}
	 else {
	     b
	}

Statement 2:

	val max = if (a > b) a else b

Here, Statement 1 and Statement 2 are same.

fun main(args: Array<String>) {
	var a = 20
	var b = 30
	val max = if (a > b) a else  b
	println("max = $max")
}

fun main(args: Array<String>) {
	var a = 20
	var b = 30
	val max = if (a > b) {
	    println("a is greater than b")
	    a
	}
	 else {
	    println("a is not greater than b")
	    b
	}
	println("max = $max")
}

Kotlin If…else…if block ladder

You can use multiple if else if block as ladder in kotlin. For example,

fun main(args: Array<String>) {
	var a = 100
	if (a < 10) {
	   println("a is smaller than 10")
	}
	else if(a < 20) {
	   println("a is smaller than 20")
	}
	else if(a < 30) {
	   println("a is smaller than 30")
	}
	else if(a < 40) {
	   println("a is smaller than 40")
	}
	else if(a < 50) {
	   println("a is smaller than 50")
	}
	else if(a < 60) {
	   println("a is smaller than 60")
	}
	else {
	   println("a is greater than or equal to 60")
	}

}

Output:
a is greater than or equal to 60

Kotlin Nested If else Block

if else block can be nested in kotlin. It means an if else block can be written inside another if else block.

fun main(args: Array<String>) {

    val a = 30
    val b = 50
    val c = -20

    val max = if (a > b) {
        if (a > c)
            a
        else
            c
    } else {
        if (b > c)
            b
        else
            c
    }

    println("max = $max")
}

Output:
max = 50

Explanation: This program calculates maximum value between a, b and c.

Conclusion

In this post, we have seen how to use kotlin if else block. Now, we clearly know that it can be used in 2 ways, Traditional way and as an Expression. In traditional way, we use it as statement. Since we can use kotlin if else block as expression, there is no ternary operator in kotlin.

Now, what next?
In the next post, you will learn about for block.