fun main(){
    val num ="10"
    val num2 = "11"
    num + num2 //->1011  字符串拼接
    var number = 10
    //number=n
    number += 15//n=n+15
    number -= 5//n=n-5
    number *= 3//n=n*3
    number /= 3//n=n/3

}