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Kotlin If...Else Expressions: Decision-Making in Code

The if...else statement is a fundamental control flow construct in Kotlin, enabling programmers to make decisions and execute different code blocks based on certain conditions. It allows for branching and conditional execution, making code more adaptable and responsive to different scenarios.

Structure of an If...Else Expression

The basic structure of an if...else statement in Kotlin is as follows:

if (condition) {

  // Code to execute if the condition is true

} else {

  // Code to execute if the condition is false

}

 

Where:

• condition is a Boolean expression that determines whether the if block or the else block is executed.

Example of an If...Else Expression

Consider a simple example of checking whether a user's age is eligible for voting:

val age = 16

if (age >= 18) {

  println("You are eligible to vote.")

} else {

  println("You will be eligible to vote in 2 years.")

}

 

In this example, the if block is executed because the age variable is greater than or equal to 18. If the age variable was less than 18, the else block would have been executed.

Nested If...Else Expressions

Nested if...else statements allow for multiple conditions to be checked within a single control flow structure. They provide a more granular way to handle different scenarios based on multiple criteria.

For instance, consider a scenario where you need to determine a discount based on both a customer's age and their purchase amount:

val age = 25

val purchaseAmount = 100.00

 

if (age >= 60) {

  if (purchaseAmount >= 50.00) {

    println("You receive a 20% discount.")

  } else {

    println("You receive a 10% discount.")

  }

} else if (age < 18) {

  println("You receive a 5% discount.")

} else {

  println("No discount applicable.")

}

 

In this example, the first if block checks if the customer's age is 60 or older. If so, a nested if block further checks if their purchase amount is 50.00 or more. If both conditions are met, a 20% discount is applied; otherwise, a 10% discount is applied. If the customer's age is less than 18, a 5% discount is applied. Otherwise, no discount is applied.

Using the When Expression as an Alternative to If...Else

The when expression provides a more concise and expressive alternative to multiple nested if...else statements, particularly when dealing with multiple conditions and corresponding actions. It offers a more structured and readable approach to handling multiple scenarios.

Consider the previous example rewritten using the when expression:

val age = 25

val purchaseAmount = 100.00

 

val discount = when {

  age >= 60 && purchaseAmount >= 50.00 -> 0.20

  age >= 60 -> 0.10

  age < 18 -> 0.05

  else -> 0.00

}

 

println("Discount percentage: $discount")

 

The when expression checks each condition sequentially and applies the corresponding discount value to the discount variable. It provides a more compact and readable way to handle multiple scenarios.

Conclusion

If...else expressions and the when construct are essential tools for decision-making in Kotlin code. They allow programmers to control program flow based on various conditions, making their code more adaptable and responsive to different scenarios. By effectively utilizing these control flow structures, you can enhance the logic and functionality of your Kotlin applications.