Assignment operators

Learn shortcut assignments with =, +=, -=, *=, /= and ++/--.

Assignment operators

The = operator assigns a value to a variable. Kotlin also offers compound assignment operators: +=, -=, *=, /=, %=. These perform the operation and the assignment in a single step.

For example, x += 5 is the same as x = x + 5. You can also increment or decrement a variable by one with ++ and --.

var x = 10
x += 5      // x = 15
x -= 3      // x = 12
x++         // x = 13
x--         // x = 12

Exercise Try compound assignment

Write a fun main(). Declare var total = 10. Increment with total += 5 and print with println(total).

Show example solution

fun main() {
    var total = 10
    total += 5
    println(total)
}

Prefix and postfix ++ and --

The ++ and -- operators can come before or after the variable. ++x increments first then yields the value; x++ yields the value first then increments.

Standalone, both yield the same result. But inside an expression, they differ. So to avoid confusion, prefer standalone use.

Test yourself

Assignment operators: fill in the missing part

var x = 10
x ____= 5  // x = 15

Show answer

var x = 10
x += 5  // x = 15

What does `x += 5` do?
- Adds 5 to x
- Sets x to 5
- Multiplies x by 5
- It throws an error
Show answer

Adds 5 to x — The += operator adds 5 to x.
Assignment operators: match the terms

=

Assign
+=

Add and assign
-=

Subtract and assign
++

Increment

Next lesson: Comparison operators

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