Increment & Decrement Operators in Kotlin

In programming, increasing the value of a variable by 1 is so common, there is an operator designed to do that.

That operator is the increment operator (++):

var number = 10
number++ // short for number += 1

println(number) // Output: 11

There is also one such operator for decreasing the value of a variable by 1.

That operator is the decrement operator (--):

var number = 10
number-- // short for number -= 1

println(number) // Output: 9

Postfix:

In the examples above, we have used these two operators in their postfix form, with operator (++) after operand (number) such as number++.

If used postfix, the increment operator increments and returns the value before incrementing:

var number = 10

val oldNumber = number++

println(oldNumber) // Output: 10
println(number) // Output: 11

This code first assigns the value of number (which is 10) to oldNumber and then increments number (making it 11). It's equivalent to this:

val oldNumber = number
number++

Prefix:

However, there is also the prefix form, with operator before operand (for example, ++number).

When used prefix, the increment operator increments and returns the value after incrementing:

var number = 10

val newNumber = ++number

println(newNumber) // Output: 11
println(number) // Output: 11

This code first increments number (making it 11) and then assigns the new value of number to newNumber (making it 11). It's equivalent to this:

number++
val newNumber = number

Here's an example with the decrement operator:

var number = 10

val newNumber = --number

println(newNumber) // Output: 9
println(number) // Output: 9

Assignment
Follow the Coding Tutorial and let's practice with these operators!

Hint
Look at the examples above if you get stuck.