Control Flow in Kotlin: If-Else

1. Why Use If-Else?

Control flow statements allow a program to make decisions and execute different code paths based on conditions. In Kotlin, if and if-else statements are used to:

Perform different actions depending on conditions.
Make the code dynamic instead of executing sequentially all the time.
Handle logical decisions in algorithms, user input, or system state.
Improve readability and maintainability compared to complex nested code.

2. How to Use If-Else? (With Example)

The if statement evaluates a condition and executes code if the condition is true. You can add else to handle the false case.

fun main() {
    val number = 10

    if (number > 0) {
        println("Number is positive")
    } else {
        println("Number is zero or negative")
    }
}

Output:

Number is positive

3. Explain Each Form

3.1 Simple If

Executes a block only when the condition is true:

val age = 20
if (age >= 18) {
    println("You are an adult")
}

Output: You are an adult

3.2 If-Else

Handles both true and false conditions:

val temperature = 30
if (temperature > 35) {
    println("It's very hot")
} else {
    println("Temperature is moderate")
}

Output: Temperature is moderate

3.3 If-Else If Ladder

Check multiple conditions in sequence:

val score = 85

if (score >= 90) {
    println("Grade A")
} else if (score >= 75) {
    println("Grade B")
} else if (score >= 60) {
    println("Grade C")
} else {
    println("Fail")
}

Output: Grade B

3.4 Using If as an Expression

In Kotlin, if can return a value:

val max = if (10 > 5) 10 else 5
println("Max value: $max")

Output: Max value: 10

4. Key Points

All if statements evaluate boolean expressions.
if can be used as an expression to return a value.
Chaining else if allows checking multiple conditions in order.
Curly braces are required when executing multiple statements in a block.

5. Interview Questions

Why Use If-Else?

Why do we use if-else statements in Kotlin?
What are the benefits of using if-else over sequential statements?

How If-Else Works?

How does Kotlin evaluate if-else conditions?
Explain the difference between using if as a statement and if as an expression.