[Kotlin] 제어문 for , forEach , range , repeat , when

for in 

예 1.) ===============================================
for (i in 0..5) {
    print(i)
}

예 2.) ===============================================
val items = listOf(10, 20, 30, 40)

    for (i in items)
        println("value is $i")

//Following is printed to the console.
value is 10
value is 20
value is 30
value is 40

예 3. index 출력 "indices" ============================
val items = listOf(10, 20, 30, 40)

    for (i in items.indices)
        println("value is $i")

//Following is printed to the console:
value is 0
value is 1
value is 2
value is 3

예 4.) index 와 element 출력 "withIndex()" =============
val items = listOf(10, 20, 30, 40)

    for ((i,e) in items.withIndex())
        println("the index is $i and the element is $e")

//Following is printed on the console:
the index is 0 and the element is 10
the index is 1 and the element is 20
the index is 2 and the element is 30
the index is 3 and the element is 40

forEach   [ Range " ..  연산자 " ]

(2..5).forEach{
        println(it)
    }

//or

(2..5).forEach{
      i ->  println(i)
    }

//Following is printed on the console:
2
3
4
5

 

존재 여부 " in  , !in"

var x = 5

    if(x in 1..10)
    {
        print("x exists in range") //this gets printed
    }
    else{
        print("x does not exist in range")
    }

x = 15

    if(x !in 1..10)
    {
        print("x does not exist in range") //this gets printed
    }
    else{
        print("x does exist in range") 
    }
    

 Range ..는 역순으로 사용할 수 없음. -->  10..0 처럼 거꾸로 사용 못함.
 여기에서 downTo키워드를 사용

var x = 5

    if(x in 10 downTo 1)
    {
        print("x exists in range") //this gets printed
    }
    else{
        print("x does not exist in range")
    }

for (i in 5 downTo 0) 
print(i) //543210

마지막 요소를 제외 "until"

for (i in 1 until 4) {
     print(i)
}
//prints 123

단계적으로 범위를 탐색 "step"

for (i in 1..5 step 3) print(i) // prints 14

for (i in 4 downTo 1 step 2) print(i) // prints 42

N번 반복 실행 "repeat"

repeat(3) {
        println("Hello World!")
        println("Kotlin Control Flow")
    }

선택, 분기분 "when"

예 1.)
var num = 10
    when (num) {
        0 -> print("value is 0")
        5 -> print("value is 5")
        else -> {
            print("value is neither 0 nor 5") //this gets printed.
        }
    }
    
예 2.) until
var valueLessThan100 = when(101){
        in 1 until 101 -> true
        else -> {
            false
        }
    }
    
    print(valueLessThan100) //false
    

제어문 for , forEach , range , repeat , when