Chapter One&&Two

This Learn Swift series is designed for beginners with NO programming experience. It uses the latest version of Swift 3 and Xcode 8. 

1.swift的源文件扩展名.swift

2.不需要编写main函数，程序从上往下执行；不需要每条语句都加分号，同一行有多条代码语句是，中间必须有分号。

3.注释： / 单行注释        /* 多行注释 */       嵌套注释 ： /*   /*  注释  */    */

4.常量和变量    let声明常量    var声明变量

vara =1

varb =2

str="wangchao"

letf =10

str=String(29)

varc:Float=2.3

vard:Float=13.90

print(Int(c))

print(Int(d))

print(round(d))

print(round(c))

print(str)

print(a+b)

print(str)

vara =1

varb =2

str="wangchao"

letf =10

str=String(29)

varc:Float=2.3

vard:Float=13.90

print(Int(c))

print(Int(d))

print(round(d))

print(round(c))

print(str)

print(a+b)

print(str)

vara =1

varb =2

str="wangchao"

letf =10

str=String(29)

varc:Float=2.3

vard:Float=13.90

print(Int(c))

print(Int(d))

print(round(d))

print(round(c))

print(str)

print(a+b)

print(str)

vara =1

varb =2

str="wangchao"

letf =10

str=String(29)

varc:Float=2.3

vard:Float=13.90

print(Int(c))

print(Int(d))

print(round(d))

print(round(c))

print(str)

print(a+b)

var str = "Hello, playground"

var swiftString = "Swift is fun"

var hours = 24

var PI = 3.14

var me = ("Mars",26, "[email protected]")

me.0

me.1

me.2

定义常量，并尝试修改报错

let minute = 30

//minute = 20

let不可变，要转换成var类型

Swift根据我们赋值自动判断变量类型  type inference，我们也可以自己指定类型

var x: Int

var s: String //指定类型    type annotation

5.创建一个button

let btn = UIButton()

btn.frame = CGRect(x:100,y:100,width:100,height:100)

btn.backgroundColor = UIColor.red

self.view.addSubview(btn)

6.整数和浮点数

/* 一般使用Int就行，除非有特殊情况  如下两种情况输出相同，因为编译器对Int进行了正确的类型选择*/

Int.min

Int.max

Int64.min

Int64.max

//十六进制  八进制    二进制  十进制

let fifteenInDecimal = 15

let fifteenInHex = 0xf

let fifteenInOctal = 0o17

let fifteenInBinary = 0b1111

let million = 1_000_000 //千分位

//浮点数

var float1:Float = 1/3

var double1:Double = 1/3

//科学计数法

var pi = 31415926e-7