//: Playground - noun: a place where people can play
import UIKit
//var name: String = "hwl"
//var age:Int = 29
//var isman:Bool = true
var name = "hwl"//类型推导为String
var age = 29//类型推导为Int
var isman = true//类型推导为Bool
var π = 3.14159226//可以直接用π作为变量名更形象
var