Constants refer to fixed values
that a program may not alter during its execution. Constants can be of any of
the basic data types like an integer constant, a floating constant, a
character constant, or a string literal. There are enumeration constants
as well.
Constants are treated just like
regular variables except the fact that their values cannot be modified after
their definition.
Constants Declaration
Before you use constants, you must
declare them using let keyword as follows
let
constantName = <initial value>
Following is a simple example to
show how to declare a constant in Swift
import Cocoa
let constA = 42
println(constA)
Result:
42
Type Annotations
You can provide a type
annotation when you declare a constant, to be clear about the kind of
values the constant can store. Following is the syntax −
var
constantName:<data type> = <optional initial value>
The following example shows how to
declare a constant in Swift using Annotation. Here it is important to note that
it is mandatory to provide an initial value while creating a constant
import Cocoa
let constA = 42
println(constA)
let constB:Float = 3.14159
println(constB)
Result:
42
3.1415901184082
Naming Constants
The name of a constant can be
composed of letters, digits, and the underscore character. It must begin with
either a letter or an underscore. Upper and lowercase letters are distinct
because Swift is a case-sensitive programming language.
You can use simple or Unicode
characters to name your variables. Following are valid examples −
import Cocoa
let _const = "Hello World!"
println(_const)
Result:
Hello World!
Printing Constants
You can print the current value of
a constant or variable using println function. You can interpolate a
variable value by wrapping the name in parentheses and escape it with a
backslash before the opening parenthesis: Following are valid examples
import Cocoa
let constA = "Book"
let constB = 100.00
println("Value of \(constA) is more than \(constB) dollar")
Result:
Value
of Book is more than 100.0 dollar
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