In Scala there are no ++ or -- operators. You should instead use the += and -= operators, as shown below. First the += operator:
scala> var i = 1 i: Int = 1 scala> i++ <console>:9: error: value ++ is not a member of Int i++ ^ scala> i += 1 scala> println(i) 2
Next the -= operator:
scala> i-- <console>:9: error: value -- is not a member of Int i-- ^ scala> i -= 1 scala> println(i) 1
The reason there are no ++ or -- operators in the language has to do with "language purity"; allowing for them would have meant adding a special rule to the language, and they wanted to avoid that.