语法 ```scala object hai04 { def main(args: Array[String]): Un


object hai04 {
  def main(args: Array[String]): Unit = {
    var i = 1
    while (i<=20){
      println(i)
      i += 1
    }
    for (j <- 1 to 20 by 2 ){
      println(j)
    }
  }
}

for (j <- 1 to  20 ; if(j%2==0);if(j%3==0)){
  println(j)
}


object hai05 {
  def main(args: Array[String]): Unit = {
    val rs  = for(i <- 1 to 4)yield  {
      i*2
    }
    println(rs)
    println(rs(0))
    println(rs(1))
    println(rs(2))
  }
}