Show me ++ and -- being used in a real EK9 program.

← Operators and Expressions · Ref: Q996

The ++ and -- operators increment and decrement a variable by 1. They are standalone statements — write them on their own line.

INCREMENT:

  counter++         adds 1 to counter

DECREMENT:

  counter--         subtracts 1 from counter

OTHER MUTATION OPERATORS:

  counter += 5      adds 5 to counter
  counter -= 3      subtracts 3 from counter

All mutation operators are standalone statements. They modify the variable directly and cannot be combined with other expressions on the same line.

Example

defines module qa.operators.incrementpractice

  defines program

    IncrementDemo()
      stdout <- Stdout()

      // ++ increments by 1
      hitCount <- 0
      hitCount++
      hitCount++
      hitCount++
      stdout.println(`Hits: ${hitCount}`)

      // -- decrements by 1
      livesRemaining <- 3
      livesRemaining--
      stdout.println(`Lives: ${livesRemaining}`)

      // += adds an amount
      totalScore <- 0
      totalScore += 100
      totalScore += 250
      totalScore += 75
      stdout.println(`Score: ${totalScore}`)

      // -= subtracts an amount
      totalScore -= 50
      stdout.println(`After penalty: ${totalScore}`)

      // Counting in a loop
      evenCount <- 0
      for number in 1 ... 10
        if number mod 2 == 0
          evenCount++
      stdout.println(`Even numbers: ${evenCount}`)

Common mistakes

E50050 — ++ is a standalone statement in EK9 that does not return a value. Writing 'x <- x++' causes a duplicate variable error because ++ completes first, then <- tries to redeclare the same name.

Incorrect:

      evenCount <- evenCount++

Correct:

      evenCount++

Other ways to ask this

How do I increment a counter in EK9?
Give me a practical example of ++ in EK9
How do I use ++ and += in EK9 code?

Coming from another language?

EK9 has ++ and -- as standalone statements. They modify the variable in place. Use += and -= for adding/subtracting other amounts.

Keywords: increment, mutation, counter, statement, decrement