//
// simple program to show, for list of grades, how many A's, B's, etc.
//
// this version uses filter with a range of numbers for each letter
// grade
//
println("type in grades (integers), quit to end")
val grades = fillList()

val numA = countInRange(grades, 90, 100)
val numB = countInRange(grades, 80, 89)
val numC = countInRange(grades, 70, 79)
val numD = countInRange(grades, 60, 69)
val numF = countInRange(grades, 0, 59)

println(numA + " A")
println(numB + " B")
println(numC + " C")
println(numD + " D")
println(numF + " F")

def fillList() : List[Int] = {
  val input = readLine
  if (input == "quit")
    Nil
  else
    input.toInt::fillList()
}

// count number of elements in range from start through end
def countInRange(nums : List[Int], start : Int, end : Int) : Int = {
  nums.filter(num => (num >= start) && (num <= end)).length
}