Hitre spremenljivke, konstante in literale (z najboljšimi praksami)

V tem članku boste spoznali spremenljivke, konstante, literale in primere njihove uporabe pri programiranju Swift.

Kaj je spremenljivka?

Pri programiranju se spremenljivke uporabljajo za shranjevanje podatkov v pomnilnik, ki jih lahko uporabljamo v celotnem programu. Vsaka spremenljivka mora dobiti enolično ime, imenovano identifikator. Koristno je, da spremenljivke predstavljamo kot vsebnike, ki vsebujejo informacije, ki jih je mogoče pozneje spremeniti.

Netehnično lahko spremenljivko predstavljate kot vrečko, v katero lahko shranite nekaj knjig in te knjige lahko kasneje nadomestite z drugimi.

Kako razglasiti spremenljivke v Swiftu?

V Swiftu za razglasitev spremenljivke uporabljamo ključno besedo var .

Primer:

 var siteName: Natisni niz (siteName)

Deklarirali smo spremenljivko z imenom siteName tipa String, kar pomeni, da lahko vsebuje samo nizne vrednosti. Obiščite Swift Strings, če želite izvedeti več o strunah.

Če poskusite zagnati zgornjo kodo na igrišču, nam bo povzročila napako časa prevajanja (spremenljivka je uporabljena pred inicializacijo), ker ne shranjuje / ne vsebuje nobenih vrednosti.

Kako dodeliti vrednost spremenljivki v Swiftu?

Vrednost spremenljivki lahko dodelite s pomočjo operatorja dodelitve (=).

Primer 1: Deklariranje in dodelitev vrednosti spremenljivki

 var siteName:String siteName = "Apple.com" print(siteName)

ALI

Vrednost lahko tudi dodelite v vrstici kot

 var siteName:String = "Apple.com" print(siteName)

Ko zaženete program, bo rezultat:

 Apple.com

Spremenljivka siteName zdaj vsebuje vrednost "Apple.com".

Ker je Swift jezik, ki izhaja iz vrste, lahko samodejno sklepa (ve), da je "Apple.com", Stringin siteName označi kot String. Torej lahko celo odstranite tip (:String)iz deklaracije kot:

Primer 2: Vrednost spremenljivke vnesite v Swift

 var siteName = "Apple.com" print(siteName)

Ko zaženete program, bo rezultat:

 Apple.com

Ker je siteName spremenljivka, lahko njeno vrednost spremenite tudi tako, da preprosto uporabite operator dodelitve, vendar brez varključne besede kot:

Primer 3: Spreminjanje vrednosti spremenljivke

 var siteName = "Apple.com" // Assigning a new value to siteName siteName = "Programiz.com" print(siteName)

Ko zaženete program, bo rezultat:

 Programiz.com

Kaj je konstanta?

Konstanta je posebna vrsta spremenljivke, katere vrednosti ni mogoče spremeniti. Koristno je, da si konstante predstavljamo kot vsebnike, ki vsebujejo informacije, ki jih kasneje ni mogoče spremeniti.

Netehnično lahko konstanto predstavljate kot vrečko za shranjevanje nekaterih knjig, ki je ni mogoče zamenjati, ko jo vstavite v vrečko.

Kako razglasiti konstanto v Swiftu?

V Swiftu uporabljamo letključno besedo za razglasitev spremenljivke.

Primer:

 let siteName:String print(siteName)

Razglasili smo konstanto z imenom siteName tipa String.

Če poskusite zagnati zgornjo kodo, se nam prikaže napaka časa prevajanja (konstanta, uporabljena pred inicializacijo), ker ne vsebuje / zadržuje nobene vrednosti.

Kako dodeliti vrednost konstanti v Swiftu?

Vrednost lahko dodelite v konstanti, ki je enaka spremenljivki, z uporabo operatorja dodelitve (=).

Primer 4: Deklariranje in dodelitev vrednosti konstanti

 let siteName:String siteName = "Apple.com" print(siteName)

ALI

Vrednost lahko tudi dodelite v vrstici kot

 let siteName:String = "Apple.com"

Ko zaženete program, bo rezultat:

 Apple.com

Zdaj konstanta siteName vsebuje / zadržuje vrednost "Apple.com".

Tako kot spremenljivke lahko tudi :Stringiz deklaracije odstranite type ( ) kot:

Primer 5: Tip izpeljane konstante v Swiftu

 let siteName = "Apple.com" print(siteName)

Ko zaženete program, bo rezultat:

 Apple.com

But unlike variables, you cannot change the value of constants. So, you cannot do something as

Example 6: Changing the value of constants (Not allowed)

 let siteName = "Apple.com" siteName = "Programiz.com" //compile time error print(siteName)

Above statement gives us an error because as we said the value of a constant cannot be changed once data is stored. This is the key difference between a variable and constant.

What is a Literal?

A literal is a value that appears directly in your source code. It can be a number, character, or a string etc. For e.g: "Hello, World" , 12, 23.0, "C" are simple example of literals. Literals are often used to initialize (assign values to) variables or constants.

For example:

 let siteName = "Apple.com"

In the above expression siteName is a variable, and "Apple.com" is a literal.

Types of literals in Swift

Integer literals

It represents a decimal, binary, octal, or hexadecimal value. It has four types.

  • Binary Literals
    • Represents binary value.
    • Begins with 0b.
  • Octal Literals
    • Represents octal value.
    • Begins with 0o.
  • Hexadecimal Literals
    • Represents hexadecimal value.
    • Begins with 0x.
  • Decimal Literals
    • Represents decimal value.
    • Begins with nothing. Everything you declare in integer literal is of type decimal.

Example 7: How to use an integer literal in Swift?

 let binaryNumber = 0b11111111 print(binaryNumber) print(1231)

When you run the program, the output will be:

 255 1231

In the above program, there are two integer literals 0b11111111 (binary literal) and 1231 (decimal literal). The decimal value of 11111111 is 255, therefore the print(binaryNumber) statement outputs 255 in the screen.

Similarly print(1231) outputs decimal value 255 in the console.

String & Character literals

A string literal is a sequence of characters surrounded by double quotes and a character literal is a single character surrounded by double quotes.

Example 8: How to use string and character literal in Swift?

 let someCharacter:Character = "C" let someString:String = "Swift is awesome"

In the above program "C" is a character literal and "Swift is awesome" is a string literal.

Floating point literals

It is used to initialize variables of data type float and double. It can be of two types:

Decimal:

It can have an optional exponent, indicated by an uppercase or lowercase e. For decimal numbers with an exponent of exp, the base number is multiplied by 10exp:

Example 9: How to use decimal literals in Swift?

 let someFloat = 12.23 let someAnotherFloat = 3.14e2 print(someFloat) print(someAnotherFloat)

When you run the program, the output will be:

 12.23 314.0

In the above program 12.23 and 3.14e2 are floating point literals. 3.14e2 is expressed with exponential and is equivalent to 3.14 * 102.

Hexadecimal:

Hexadecimal floats must have an exponent, indicated by an uppercase or lowercase p.For hexadecimal numbers with an exponent of exp, the base number is multiplied by 2exp:

Example 10: How to use hexadecimal literals in Swift?

 let someFloat = 0xFp10 let someAnotherFloat = 0xFp-12 print(someFloat) print(someAnotherFloat)

When you run the program, the output will be:

 15360.0 0.003662109375

In the above program 0xFp10 and 0xFp-12 are floating point literals. 0xFp10 is expressed with exponential and equivalent to 15*210 (F is represented as 15 in decimal). Therefore, print(someFloat) outputs 15360.0 in the screen.

Likewise, 0xFp-12 is equivalent to 15 * 2-12. Therefore, print(someAnotherFloat) outputs 0.003662109375 in the screen.

Boolean Literals

There are two boolean literals in swift. They are true and false..

Example 11: How to use Boolean literals in Swift?

 let result:Bool = false

In the above program, false is a Boolean literal which is assigned to the constant result.

Rules and Best practices for variables and constants

  1. Choose a name that makes sense. For example, var name makes more sense than var n.
  2. Use camelCase notation to declare a variable or a constant. Camel-case notation starts with lowercase letter. For example: 
     var studentName let studentAge let address
  3. You can also define variables and constants without labeling it. Not labeling with name means you are not going to use it in the program. There are many cases where you want to create a unused variable. In that case you can use _ placeholder as: 
     var _ = "Apple.com"//string initialized but not stored in a variable let _ = "Apple.com"
    Or even this is valid 
     _ = "Apple.com"
  4. Use constants if you only need to set a value once and never need to change it again during a program. However, if you do need to change it at a later point, use variables.
  5. Imena konstant in spremenljivk ne smejo vsebovati presledkov, matematičnih simbolov, puščic, kodnih točk Unicode za zasebno uporabo ali znakov za risanje črt in okenc. Prav tako se ne morejo začeti s številko, čeprav so številke morda vključene drugje znotraj imena.
    Primer: 
     var 12 = "Apple.com" // daje napako pri prevajanju: pričakovani vzorec var @hello = “Hello” // daje napako pri prevajanju: pričakovani vzorec

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