swift3-常量与变量，int、float、double，类型推导

概述1.变量 //变量var str = "Hello, playground"var dd = 23var PI = 3.14var uu = truevar me = ("me",11,"33")me.0me.1me.2PI = 3.12 2.常量 //常量let m = 89let u = falsevar a:Intvar b:Stringprint 1.变量

//变量var str = "Hello,playground"var dd = 23var PI = 3.14var uu = truevar me = ("me",11,"33")me.0me.1me.2PI = 3.12

2.常量

//常量let m = 89let u = falsevar a:Intvar b:Stringprint(a) //a 还没有初始化，不能使用

3.int、float、double

Int.min     //-9223372036854775808Int.max     //9223372036854775807Int64.min   //-9223372036854775808Int64.max   //9223372036854775807let f = 15      //15let fa = 0xF        //15let fb = 0o17       //15let fc = 0b1111     //15let fd = 1_000_000      //1000000var oneThirdint = 1/3   //默认类型int,0var oneThirdfloat:float = 1/3   //小数点后有7位,0.3333333var oneThirdDouble:Double = 1/3  //小数点后有16位,0.3333333333333333print(oneThirdint)  //0\nprint(oneThirdfloat)    //由打印可知，精确度为小数点后6位,0.333333\nprint(oneThirdDouble)   //精确度为小数点后15位,0.333333333333333\n

4.查看推导类型type(of:XXX)

var three = 3type(of:three)  //查看推导结果,Int.Typevar z = 0.14type(of:z)  //Double.Typevar PI = 314e-2     //3.14PI = 3 + 0.14159    //3.14159PI = Double(three) + z  // 不同类型变量不能直接加减,要先类型转换，3.14

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