Kotlin if Statement

Introduction

The if statement is a fundamental control flow statement in Kotlin that allows you to execute a block of code based on a specified condition. This chapter will cover the syntax and usage of the if statement, if-else statement, and if-else if-else statement with detailed explanations and examples.

1. if Statement

The if statement is used to execute a block of code only if the specified condition is true. It is one of the most basic forms of decision-making in programming.

Syntax

if (condition) {
    // Code to execute if condition is true
}

• condition: A Boolean expression that evaluates to either true or false.
• block of code: The set of instructions that will be executed if the condition is true.

Example

fun main() {
    val a = 10
    if (a > 5) {
        println("a is greater than 5")
    }
}

Explanation:

• val a = 10: Declares a variable a and initializes it with the value 10.
• if (a > 5): Checks if the value of a is greater than 5. Since 10 is greater than 5, the condition is true.
• { println("a is greater than 5") }: This block of code is executed because the condition is true, printing "a is greater than 5" to the console.

2. if-else Statement

The if-else statement provides an alternative block of code to execute if the specified condition is false. This allows you to define two different paths of execution based on the condition.

Syntax

if (condition) {
    // Code to execute if condition is true
} else {
    // Code to execute if condition is false
}

• else: Specifies the block of code to be executed if the condition is false.

Example

fun main() {
    val a = 10
    if (a > 15) {
        println("a is greater than 15")
    } else {
        println("a is not greater than 15")
    }
}

Explanation:

• if (a > 15): Checks if the value of a is greater than 15. Since 10 is not greater than 15, the condition is false.
• { println("a is greater than 15") }: This block is skipped because the condition is false.
• else { println("a is not greater than 15") }: This block is executed because the condition is false, printing "a is not greater than 15" to the console.

3. if-else if-else Statement

The if-else if-else statement allows you to test multiple conditions, executing different blocks of code for each condition. It is useful when you have several conditions to check.

Syntax

if (condition1) {
    // Code to execute if condition1 is true
} else if (condition2) {
    // Code to execute if condition2 is true
} else {
    // Code to execute if none of the conditions are true
}

• else if: Specifies a new condition to check if the previous condition(s) are false.
• else: Specifies the block of code to execute if none of the conditions are true.

Example

fun main() {
    val a = 10
    if (a > 15) {
        println("a is greater than 15")
    } else if (a > 5) {
        println("a is greater than 5 but not greater than 15")
    } else {
        println("a is not greater than 5")
    }
}

Explanation:

• if (a > 15): Checks if a is greater than 15. Since 10 is not greater than 15, this condition is false.
• else if (a > 5): Checks if a is greater than 5. Since 10 is greater than 5, this condition is true.
• { println("a is greater than 5 but not greater than 15") }: This block is executed because the second condition is true, printing "a is greater than 5 but not greater than 15" to the console.
• The else block is skipped because one of the conditions was true.

Using if as an Expression

In Kotlin, if can also be used as an expression that returns a value. This is useful when you want to assign a value based on a condition.

Syntax

val result = if (condition) {
    // Code to execute if condition is true
    value1
} else {
    // Code to execute if condition is false
    value2
}

• The if expression evaluates to value1 if the condition is true, and to value2 if the condition is false.

Example

fun main() {
    val a = 10
    val b = 20

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

    println("The maximum value is $max")
}

Explanation:

• val max = if (a > b) { a } else { b }: Evaluates the condition a > b. Since 10 is not greater than 20, the condition is false. Therefore, max is assigned the value of b, which is 20.
• println("The maximum value is $max"): Prints "The maximum value is 20" to the console.

Nested if Statements

You can nest if statements inside other if statements to check multiple conditions. This allows for more complex decision-making.

Syntax

if (condition1) {
    // Code to execute if condition1 is true
    if (condition2) {
        // Code to execute if condition1 and condition2 are true
    }
}

Example

fun main() {
    val a = 10
    val b = 5

    if (a > 5) {
        println("a is greater than 5")
        if (b < 10) {
            println("b is less than 10")
        }
    }
}

Explanation:

• if (a > 5): Checks if a is greater than 5. Since 10 is greater than 5, this condition is true.
• { println("a is greater than 5") }: This block is executed because the condition is true, printing "a is greater than 5".
• if (b < 10): Checks if b is less than 10. Since 5 is less than 10, this condition is true.
• { println("b is less than 10") }: This block is executed because the nested condition is true, printing "b is less than 10".

Conclusion

In this chapter, you learned about the if statement in Kotlin, including its syntax and usage with if-else and if-else if-else constructs. You also saw how to use if as an expression and how to nest if statements. Understanding how to use the if statement is crucial for making decisions and controlling the flow of your Kotlin programs.