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# Scala Odd and Even Numbers

Use modulo division to test for even and odd numbers. Call filter to generate sequences of even and odd values.
Odd, even. 1 is odd. 2 is even. We all know this, but how do we compute this? With Scala we use modulo division to see if 2 divides a number evenly (with no remainder).
With def, we define two small functions that return Booleans. With isEven we return true if a number is evenly divisible by 2. And with isOdd we do the opposite.
Example methods. Let us begin. With isEven we use a short syntax form in Scala to return whether the modulo division of a number by 2 equals 0. With isOdd we simply return "not isEven."

List.range: We invoke this method to get a short list of numbers to test. We test each Int for even and odd status.

Scala program that test seven, odd numbers // These functions test for even and odd numbers. def isEven(number: Int) = number % 2 == 0 def isOdd(number: Int) = !isEven(number) // Generate a range of numbers to test. val tests = List.range(-2, 10) // Loop over numbers and indicate whether they are even or odd. for (n <- tests) { print(n) if (isEven(n)) { println(" -> Even") } if (isOdd(n)) { println(" -> Odd") } } Output -2 -> Even -1 -> Odd 0 -> Even 1 -> Odd 2 -> Even 3 -> Odd 4 -> Even 5 -> Odd 6 -> Even 7 -> Odd 8 -> Even 9 -> Odd
Filter, generate sequences. Let us add some complexity. We repeat our isEven and isOdd numbers. We use Seq.range and then filter() to generate sequences of even and odd numbers.

FilterNot: We use filterNot with isEven to generate odd numbers—this is another way of generating odds.

Scala program that uses filter on even, odd numbers // Tests parity of numbers. def isEven(number: Int) = number % 2 == 0 def isOdd(number: Int) = !isEven(number) // Generate even numbers. println("Filter even") val evens = Seq.range(0, 10).filter(isEven(_)) println(evens) // Generate odd numbers. println("Filter odd") val odds = Seq.range(0, 10).filter(isOdd(_)) println(odds) // Another way to get odd numbers. println("Filter not even") val odds2 = Seq.range(0, 10).filterNot(isEven(_)) println(odds2) Output Filter even List(0, 2, 4, 6, 8) Filter odd List(1, 3, 5, 7, 9) Filter not even List(1, 3, 5, 7, 9)
A review. Testing a number's parity is simple. And with methods like filter and filterNot we can generate ranges of numbers based on their parity.