if expression

Learn to use if as an expression in Kotlin.

The if expression

In Kotlin, if is not only a statement but also an expression. It can return a value. This replaces Java's ternary operator (?:).

val age = 20
val status = if (age >= 18) "Adult" else "Child"
println(status)  // Adult

When used as an expression, each branch must return a value and else is required. The value can be assigned to a variable or passed directly to a method.

This form is shorter and cleaner; it is preferred for simple two-way choices.

Exercise Assign status with an if expression

Write a fun main(). Assign 20 to val age. Write val status = if (age >= 18) "Adult" else "Child". Print the result with println(status).

Show example solution

fun main() {
    val age = 20
    val status = if (age >= 18) "Adult" else "Child"
    println(status)
}

Statement vs expression

It is important to distinguish the statement and expression forms of if. As a statement, it returns no value; it just runs a block.

// Statement: no value
if (x > 0) { println("Positive") }

// Expression: returns a value
val sign = if (x > 0) "+" else "-"

In the expression form, branch types must match. if (x > 0) 1 else "a" is a compile error; one branch is Int, the other String.

Blocks can also return values: val r = if (x > 0) { compute() } else { 0 } — the last expression of the block is the value.

Test yourself

Complete the else branch

val status = if (age >= 18) "Adult" ____ "Child"

Show answer

val status = if (age >= 18) "Adult" else "Child"

Match the if forms

if (x) { ... }

Statement
val s = if (x) a else b

Expression
else if

Chain branch
if without else

Conditional block
Why is else required in an if expression?
- Because each branch must return a value
- For the curly braces
- No compile error otherwise
- For performance
Show answer

Because each branch must return a value — As an expression, each branch must produce a value; without else it is incomplete.

Next lesson: when

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