我的kotlin学习之旅-day1-2020-12-20

每天一小时或者更多，慢慢解锁一下kotlin编程，day1先敲一下基础知识。

package day1

fun main(args:Array<String>){
    println("Kotlin start...")
    whenFunction(1);
    whenFunction("kotlin");
    whenFunction('X')
    whenFunction("aaa")
    val result = fact(10);
    println(result)
    forFunction()
    val res = forFact(10)
    println(res)
    whileFunction()
    returnFunction()
}


/**
 * case when
* when的用法，参数可以是任意类型
 */
fun whenFunction(obj:Any?){
    val invalide = arrayOf(11,12,13);
    when(obj){
        1,2,3,4,5,6,7,8,9,0 -> println("Object input is 数字！")
        "kotlin" -> println("The input is $obj")
        is Char -> println("This is a char")
        in 1..10 -> println("obj is in 1...10")
        in invalide -> println("obj is in invalide")
        !in 10..20 -> println("Obj is outside 10..20")
        else -> println("obj is $obj")
    }
}

/**
 * 用when 求阶乘
 */
fun fact(n:Int):Int{
    var result = 1;
    when(n){
        0,1 -> result = 1;
        else -> result = n * fact(n-1)
    }
    return  result;
}

/**
 * for循环的代码
 */
fun forFunction() {
    val arr = arrayOf(1,2,3);
    for (i in arr.indices) {
        println("index is $i,value is "+arr.get(i));
        println(arr[i])
    }
    for ((index, value) in arr.withIndex()){
        println("index is $index,value is $value")
    }
    (1..10).forEach {
        println(it)
    }
}

/**
 * params n
 * @return Long
 * 计算0到n到阶乘到和
 */
fun forFact(n:Int):Long {
    var result:Long = 0;
    (0..n).forEach {
        result += fact(it);
    }
    return result;
}

fun whileFunction() {
    var n = 0;
    while (n<100) {
        n++
        if (n%6==0) {
            println("I am happy")
        } else if (n%9==0) {
            println("I am continue")
            continue
        } else if (n>98) {
            println("I am break")
            break;
        }
    }
}

/**
 * return的特殊用法
 */
fun returnFunction(){
    fun sum(a:Int,b:Int) = a+b;//返回a+b的值
    println(sum(1,2))
    fun sum1(a:Int,b:Int) = {a+b}//带上大括号表示一个函数，将sum1函数返回
    println(sum1(1,2))
    println(sum1(1,2).invoke())//执行sum1函数
    val arr = arrayOf(1,2,3,4)
    arr.forEach (fun(a:Int){
        if (a==3) return@forEach;//不会结束循环，而是继续下一步循环，类似continue
        println(a)
    } )
    arr.forEach here@{
        if (it==3) return@here;//不会结束循环，而是继续下一步循环，类似continue
        println(it)
    }
}