Kotlin process control and circulation

One 、 Process control

1.if

val i = 1
if (i > 0) {
    print("Big")
} else {
    print("Small")
}

  Use if, assignment .

val i = 1
val message = if (i > 0) "Big" else "Small"

print(message)

 

fun getLength(text: String?): Int {
  return if (text != null) text.length else 0
}

  Abbreviation above ,Elvis expression ;

fun getLength(text: String?): Int {
  return text?.length ?: 0
}

 2.when

val i: Int = 1

when(i) {
    1 -> print(" One ")
    2 -> print(" Two ")
    else -> print("i  Not one nor two ")
}

 

val i: Int = 1

val message = when(i) {
    1 -> " One "
    2 -> " Two "
    else -> "i  Not one nor two " //  If you remove this line , Will report a mistake 
}

print(message)

Two 、 loop

1、for

 val oneToThree = 1..3
    for (i in oneToThree) {
        println(i)
    }

    for (i in 6 downTo 0 step 3) {
        println(i)
    }

    for (i in 0..10) {
        println(i) //012345678910
    }
    for (i in 0 until 10) {
        println(i) //0123456789
    }
    for (i in 0..10 step 2) {
        print(i) //0 2 4 6 8 10
    }
    // Get elements 
    var abc = listOf("a", "b", "c")
    for (i in abc) {
        print(i)
    }
    //     Get subscript 
    for (index in abc.indices) {
        print("$index") // 0 1 2
    }
    //     Get elements and Subscripts 
    for ((index, value) in abc.withIndex()) {
        print("$index:$value ")  //0:a 1:b 2:c
    }

 2、while

var i = 0
while (i <= 2) {
    println(i)
    i++
}

var j = 0
do {
    println(j)
    j++
} while (j <= 2)