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

#!ek9
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

E07950 — ++ is a standalone statement in EK9 that does not return a value, so it cannot be used on the right of an assignment such as 'otherCount <- evenCount++'. Write 'evenCount++' on its own line. See ek9 -h E07950 for details.

Incorrect:

      otherCount <- 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: counter, decrement, increment, mutation, statement