1. Constants & Variables

Simple experience

// 定义变量var i = 10println(i)i = 15println(i)let j = 20// 常量一经定义不能自改数值// j = 25println(j)

• Periodic summary
  • varDefine variables that can be modified after they are set
  • letDefines constants that cannot be modified after they are set
  • Do not use at end of statement;
  • In Swift, use println() an alternative in OCNSLog
  • printlnPerformance is better and will be demonstrated later

Defined OCObject

 //materialized view let v = uiview (frame: cgrectmake (0, 0, 100, 100)) //set background color V.backgroundcolor = uicolor.redcolor () //added to root view View.addsubview (v)           

• Periodic summary
  • In the Swift format that you want to instantiate an object 类名() with, the OC equivalent in alloc/init
  • OCinitWithXXX Swift can be used to 类名(XXX: ) find the corresponding function in the
  • OCA [UIColor redColor] class method in which Swift you can usually 类名.XXX find the corresponding function in the
  • Use let adornments v and assign values to indicate该常量的内存地址不允许修改，但是可以修改其内部的属性
  • The properties of the current object, which do not need to useself.

Constants & Variables Use principle: Try to use let first, only need to change, then use Var, can be more secure

Variable type

 let x = 10 let y = 10.5let z: double = 20println ( Double (x) + y) println (x + int (y))  println (y + z)              

• Periodic summary
  • In the first contact, the Swift var let Swift type is very loose because of a simple mistake.
  • In fact, the exact type of all variables is automatically deduced at the same time as the assigned value.
  • Swiftis a very strict type of language,一个值永远不会被自动转换成其他类型
  • If you want to convert, you must display the conversion in Swift
    • Decimal default is Double type
    • Integer default is Int type
  • If you want to explicitly specify the type of a variable, you can define it by using thevar 变量名: 类型 = 值

1. Constants & Variables