Brze varijable, konstante i literale (s najboljim praksama)

U ovom ćete članku naučiti o varijablama, konstantama, literalima i njihovim slučajevima upotrebe u Swift programiranju.

Što je varijabla?

U programiranju se varijable koriste za pohranu podataka u memoriju koji se mogu koristiti tijekom cijelog programa. Svaka varijabla mora dobiti jedinstveni naziv koji se naziva identifikator. Korisno je varijable smatrati spremnicima koji sadrže informacije koje se kasnije mogu mijenjati.

Netehnički, varijablu možete smatrati torbom za čuvanje nekih knjiga u njoj, a te knjige kasnije možete zamijeniti drugim knjigama.

Kako deklarirati varijable u Swiftu?

U Swiftu koristimo ključnu riječ var za deklariranje varijable.

Primjer:

 var siteName: ispis niza (siteName)

Proglasili smo varijablu pod nazivom siteName tipa String, što znači da može sadržavati samo niz vrijednosti. Posjetite Swift Strings da biste saznali više o žicama.

Ako pokušate pokrenuti gornji kôd na igralištu, dat će nam pogrešku vremena kompajliranja (varijabla se koristi prije inicijalizacije) jer ne pohranjuje / ne sadrži nikakve vrijednosti.

Kako dodijeliti vrijednost varijabli u Swiftu?

Vrijednost možete dodijeliti varijabli pomoću operatora dodjele (=).

Primjer 1: Deklariranje i dodjeljivanje vrijednosti varijabli

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

ILI

Vrijednost također možete dodijeliti kao

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

Kada pokrenete program, izlaz će biti:

 Apple.com

Varijabla siteName sada sadrži vrijednost "Apple.com".

Budući da je Swift jezik na osnovu kojeg se može zaključiti, on automatski može zaključiti (znati) da je "Apple.com" naziv a Stringi proglasiti siteName kao String. Dakle, čak možete ukloniti tip (:String)iz deklaracije kao:

Primjer 2: Uključena varijabla u Swiftu

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

Kada pokrenete program, izlaz će biti:

 Apple.com

Budući da je siteName varijabla, njezinu vrijednost možete promijeniti i jednostavnim korištenjem operatora dodjele, ali bez varključne riječi kao:

Primjer 3: Promjena vrijednosti varijable

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

Kada pokrenete program, izlaz će biti:

 Programiz.com

Što je konstanta?

Konstanta je posebna vrsta varijable čija se vrijednost ne može mijenjati. Korisno je konstante smatrati spremnicima koji sadrže informacije koje se kasnije ne mogu mijenjati.

Netehnički, konstantu možete smatrati torbom za pohranu nekih knjiga, a one se ne mogu zamijeniti kad se jednom stave u vreću.

Kako proglasiti konstantu u Swiftu?

U Swiftu koristimo letključnu riječ za deklariranje varijable.

Primjer:

 let siteName:String print(siteName)

Proglasili smo konstantu s imenom siteName tipa String.

Ako pokušate pokrenuti gornji kod, dat će nam pogrešku vremena kompajliranja (konstanta korištena prije inicijalizacije) jer ne sadrži / ne sadrži nikakvu vrijednost.

Kako dodijeliti vrijednost konstanti u Swiftu?

Vrijednost možete dodijeliti konstanti istoj varijabli pomoću operatora dodjele (=).

Primjer 4: Deklariranje i dodjeljivanje vrijednosti konstanti

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

ILI

Vrijednost također možete dodijeliti kao

 let siteName:String = "Apple.com"

Kada pokrenete program, izlaz će biti:

 Apple.com

Sada konstanta siteName sadrži / ima vrijednost "Apple.com".

Kao i varijable, možete ukloniti tip ( :String) iz deklaracije kao:

Primjer 5: Tip zaključena konstanta u Swiftu

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

Kada pokrenete program, izlaz će biti:

 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. Nazivi konstanti i varijabli ne mogu sadržavati razmake, matematičke simbole, strelice, Unicode kodne točke za privatnu upotrebu ili znakove za crtanje linija i okvira. Oni također ne mogu počinjati s brojem, iako brojevi mogu biti uključeni negdje drugdje unutar imena.
    Primjer: 
     var 12 = "Apple.com" // daje pogrešku pri kompajliranju: očekivani obrazac var @hello = “Hello” // daje pogrešku pri kompajliranju: očekivani obrazac

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