object Array_opt {

  def main(args: Array[String]) {

    // init an array
val array = new Array[String](3)
    val arr = Array(1, 2, 3, 4)

    // traversal element
    // method 1
for (i <- 0 until arr.length) {
      print(arr(i))
    }
    // method 2
for (ele <- arr) {
      println(ele)
    }
    // method 3
 
for (i <- 0 to arr.length - 1) println(arr(i))
    // get element use () replace []
println(arr(0))
    // method 4:use foreach
arr.foreach(println)
    // use exp: for(ele <- arr if(exp)) yield change to a new array
val newArr = for (ele <- arr if ele % 2 == 0) yield ele
    newArr.foreach(println)

    // ------------  buffered array -----------------------
 
val buf = ArrayBuffer[Int]()
    // add element
buf += 1
// add an array
buf +=(2, 3)
    println(buf.getClass) //class scala.collection.mutable.ArrayBuffer
buf ++= Array(4, 5, 6)
    for (value <- buf) {
      if (value >= 3) println(value)
    }
    // change into array
buf.toArray
// array change into ArrayBuffer
 
arr.toBuffer
// filter map
    //def filter(p: A => Boolean): (apply every element in array)
buf.filter(_ % 2 == 0).map(_ * 2).foreach(println)
    for (ele <- buf if ele % 2 == 0) yield ele * 2
// get sum
println(buf.sum)
    println(Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).sum) //55
println(buf.mkString("-"))
    // start , separate ,end
println(buf.mkString("<", ",", ">")) //<1,2,3,4,5,6>
for (i <- 1 to 2; j <- 1 to 2 if (i != j)) println(i * 10 + j)

    def fac(n: Int): Int = if (n <= 0) 1 else n * fac(n - 1)
    println(fac(3))

    def makeString(s: String, left: String = "[", right: String = "]") = left + s + right

  }
}