import UIKit var str = "Hello, playground" // 显式定义浮点型常量 let PI:Float = 3.141592612312312 let PI2:Double = 3.14123456789123123123 // 隐式定义浮点型变量 var randomFloat = 12312.123323 var randomDouble = 2.3793758374597349879374 // 只要理解浮点型就是有小数点的就可以了..
原文：http://www.cnblogs.com/Rinpe/p/5050458.html