swift基础（一）：常量和变量、数据类型、数据转换基础等

目录：

1.playground

2.常量和变量

3.数据类型

4.swift中的字符串

5.元祖数据类型

6.nil的应用

7.类型别名：自定义类型

8.数据转换基础

//1.playground

//: Playground - noun: a place where people can play

本示例都用Playground调试，用xcode的playground来学习基础语法，不用编译方便调试并查看结果。

新建Playgroud:File->New->Playground

//2.常量和变量

let para_constant ="常量";

var para_var ="变量";

print(para_constant);

print("par1=\(para_constant),par1=\(para_var)");

//3.数据类型

var varDouble =3.454;//默认double

var varFloat:Float  =3.4;//定义float

var varInt =234;//默认int ,64位系统等于int64,32位是int32

var varInt32:Int32 =343434;//Int32

var varDemicalInt =23;//十进制

var varBinaryInt =0b1010;//二进制

var varOctalInt =0o45;//八进制

var varHexInt =0x3298;//16进制

var varIntBigData =1_000_000;//增加下划线，增加可读性

var varBool:Bool =true;

if(varBool)

{

    print(varIntBigData);

}

else

{

    print("false");

}

//4.swift中的字符串

var varStr1 ="";

let varStr ="ert";

let upperStr =varStr.uppercaseString;//大写

let lowerStr =upperStr.lowercaseString;//小写

print("\0");//转义字符：\

let varUnicode1 ="\u{41}";//单字节Unicode

let varUnicode2 ="\u{2600}";//双字节Unicode

let varUnicode4 ="\u{0001F496}";//4字节Unicode

if(varUnicode1==varUnicode2)

{

    print("equal!")

}

else

{

    print("unequal");

}

let varCon =varUnicode1+varUnicode2;//连接字符串：+ +=

for chinvarStr.characters//遍历字符串输出单个字符

{

    print(ch);

}

print(varStr.characters.count);//统计字符串字符个数

for chinvarStr.unicodeScalars//输出Unicode编码

{

    print(ch.value);

}

//5.元祖数据类型

let letGroup1 = ("fly",123,1.2);

let letValueInt =9994;

let letValueStr ="letStr0";

let letGroup2 = (letValueInt,letValueStr,12670);

let (let1,let2,let3) =letGroup2;

print(let1);

print(let2);

print(let3);

let (_,let4,_) =letGroup1;

print(let4);

let letGroup3 = (para1:123,para2:"dfg",para3:4.5);

print(letGroup3.para2);

//6.nil的应用

var varInt1:Int? =nil;//赋值为空

print(varInt1);

varInt1 =5566;

var varBool1:Bool?;//默认为nil

print(varBool1);

//7.类型别名：自定义类型

typealias myInt =Int;//类似C语言typedef

var varint3:myInt =345;

//8.数据转换基础

var varStr3 ="1234";

var varInt4:Int? =Int(varStr3);

var varStr4 ="ab1234";

var varInt5:Int? =Int(varStr4);

var varInt6 =445454;

var varStr5 =String(varInt6);