Constants and variables for 3.Swift

1. Definition

• letDefine constants that are not allowed to be modified once they are assigned, more secure
• varDefine variables that can still be modified after assignment

• You should select constants as much as possible before you need to modify them tovar
• In Xcode 7.0, if the variable is not modified, Xcode will prompt to change tolet

Code Demo

ImportUIKit ClassViewcontroller:Uiviewcontroller{ OverrideFuncViewdidload () { Super.Viewdidload() Demo() } FuncDemo () { //Define a constant and assign a value directly LetA =10 //Constants have been assigned values,Cannot be modified,Otherwise it will be an error A =20 //Define the constant type in the assignment first //Yellow warningSwiftThe new features,You are prompted to use this constant,If not applicable,Recommend that you use"_"To replace LetB:Int b =20 //Defining variables Varc =20         // variable definition can still be modified Value         C = 30    } }

2. Data typeThe default type of integer default type is int long decimal is double cgfloat single precisionshortcut key: Option+caps Lock View Interpretation3. Automatic derivationThe type of data in Swift is deduced automatically, depending on = right to determine the specific type of data

• Swift can deduce the exact type of the variable according to the code on the right.
• Typically at development time, you do not need to specify the type of the variable
• If you want to specify a variable, you can use it after the variable name:, and then follow the class of the variable

4. Type conversionSwift is a very strict type of validation language different types of data cannot be calculated directlyimplicit type conversions are not supportedto perform a calculation, you must make a forced type conversion 

//Forcing type conversions Letx2 =100 let y2 = 10.5                 let double (x2) + y2 Let num2 = x2 + Int(y2)

 5. Output function PrintFormat: Print (object)6. Specification writing code: Operators need to add spaces apart

Constants and variables for 3.Swift