swift基础---1.简单值

//  Created by he hongwei on 16/10/13.
//  Copyright © 2016年 he hongwei. All rights reserved.
//
import Foundation

print("Hello, World!")
/*
 小细节:1. = 左右两边都要空一格,否则会报错
 
 
 */
// 1.不指定类型时,系统根据第一次初始化的值识别类型
let constNB = 32
var mutableNB = 23
mutableNB = 54
// 2.常量显性指定类型
let a:Float = 4
// 3.打印都不用@或者""了呢,直接对象就行
print(a)
// 4.值永远不会被隐式转换为其他类型。如果你需要把一个值转换成其他类型，请显式转换。
let sum = constNB + Int(a)
print(sum)
let label = "this sum is"
let labelWidth = label + String(sum)
print(labelWidth)
// 5.有一种更简单的把值转换成字符串的方法：把值写到括号中，并且在括号之前写一个反斜杠
let apple = 3
let orange = 4.8
let appleSummary = " I have \(apple) appples"
let fruitSummarr = " In total \(apple + Int(orange)) fruit "
print(appleSummary)
print(fruitSummarr)
// 6.用[]创建数组和字典,并用下标或者key来访问元素,最后一个元素后面允许有逗号
var array = ["apple", "pear", "grape" ,"orange"]
array[2] = "peach"
print(array[2])
var dictionary = ["china":"beijing","America":"washington"]
print(dictionary["china"])
// 7.通过初始化创建空数组和字典
let emptyArr = [String]()
let emptyDic = [String:Float]()
// 8.可以用[]和[:]创建空数组和空字典-----就像声明变量或者给函数传参数的时候一样
array = []
dictionary = [:]
print(array.count,dictionary.count)

参考网址[swift初见](file:///Users/hehongwei/Desktop/Swift%20初见（A%20Swift%20Tour）%20-%20The%20Swift%20Programming%20Language%20中文版%20-%20极客学院Wiki.webarchive)