Author: saqibkhan

Swift Data Types

Swift has built-in types like Int, Double, Bool and String.

Swift uses type inference to deduce the type from the value.

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Basic Types

Declare constants with let and variables with var.

Swift infers the type from the initial value.

Example

let anInt = 42           // Int
let aDouble = 3.14       // Double
let isSwiftFun = true    // Bool
let greeting = "Hello"    // String
print(aDouble)
print(isSwiftFun)
print(greeting)

This example declares common Swift types and prints them.

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Type Inference vs Annotation

Swift usually infers the type from the initial value, but you can add a type for clarity.

Example

let inferred = 10          // Int (inferred)
let annotated: Double = 3  // Double (explicit)
print(type(of: inferred), type(of: annotated))

This example contrasts inferred vs. explicit types.

Swift Variables in Real-Life

Use variables to track values like counters, flags, and user input.

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Example: Counter

Use a variable to track a counter and print it as it changes.

Example

var count = 0
count += 1
print("Count: \(count)")

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Example: Greeting

Store a value in a variable and use interpolation to print it.

Example

var name = "Kai"
print("Hello, \(name)!")
name = "Elisabeth"
print("Hello, \(name)!")

This example updates a variable and prints the new greeting.

Swift Constants

Use let to declare constants that don’t change.

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Declare Constants

Use let to bind a value once so it cannot be reassigned later.

Example

let pi = 3.14159
let maxCount = 100
// pi = 4.0 // Error: cannot assign to value: 'pi' is a 'let' constant

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Constants and Collections

If an array is bound with let, you can’t mutate (change) it.

Example

var nums = [1, 2]
nums.append(3)       // OK: nums is var
print(nums)

let fixed = [1, 2]
// fixed.append(3)  // Error if uncommented: cannot use mutating member on immutable value

Binding with let is immutable, so you can’t mutate it.

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Swift Identifiers

Identifiers name variables, constants, types, functions, etc.

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Rules for Identifiers

Identifiers must:

• Start with a letter or underscore.
• May include numbers after the first character.
• Avoid keywords unless escaped with backticks.

They can contain Unicode and must not start with a number.

Example

let name = "Swift"
let π = 3.14
let _hidden = true

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Escaping Keywords and Unicode

Escape keywords with backticks when needed, and remember identifiers can include Unicode characters.

Example

let switch = "ok"   // escape a keyword using backticks
let 🐶 = "dog"          // Unicode identifier
print(switch, 🐶)

Use backticks to escape reserved words in identifiers, and remember Swift identifiers can include Unicode characters.

Swift Multiple Variables

Declare multiple variables or constants on one line when they share a type.

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Multiple Variables Declared

Declaring multiple variables or constants on one line is only recommended if it stays easy to read.

Example

var x = 1, y = 2, z = 3
let a = 10, b = 20
print(x, y, z, a, b)

This example declares multiple variables and constants on one line.

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With Type Annotations

Use explicit types when inference could be ambiguous or to document intent.

Example

var i: Int = 1, j: Int = 2
let firstName: String = "Robin", lastName: String = "Refsnes"
print(i + j, firstName, lastName)

This example declares multiple variables and constants on one line.

Swift Print Variables

Print values with concatenation or string interpolation.

Use \(value) to insert values. You can set a separator and a terminator.

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Concatenation and Interpolation

Use concatenation to combine strings and interpolate to embed values inside strings.

Example

let first = "Hello"
let second = "Swift"
// Concatenation
print(first + ", " + second)
// Interpolation
print("\(first), \(second)")

let a = 2, b = 3
print("a = \(a), b = \(b), sum = \(a + b)")

This example shows concatenation and interpolation.

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Custom Separator and Terminator

Set a separator between items and a terminator at the end.

Example

let a = 1, b = 2, c = 3
print(a, b, c, separator: ", ", terminator: "; ")
print("done")  // prints on the same line after a semicolon

This example sets a comma-space separator and a semicolon terminator.

Swift Variables

Declare constants with let, variables with var, and use type inference or annotations as needed.

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Constants and Variables

Declare constants with let and variables with var.

Constants cannot be reassigned.

Example

let constant = 10
var counter = 0
counter += 1
// constant = 12 // Error if uncommented
print(constant, counter)

This example shows that var can change while let cannot.

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Swift Type Inference

Swift infers types automatically when possible, but you can also use annotations for clarity.

Example

let x = 10
let y: Int = 20
print(x, y)

This example shows that Swift infers types automatically when possible, but you can also use annotations for clarity.

Swift Data Types will be covered in more detail in the Swift Data Types chapter.

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Optionals

Use ? to declare values that may be nil.

Example

var nickname: String? = nil
nickname = "KJ"
print(nickname ?? "none")

This example shows an optional that may be nil.

Swift Comments

Use comments to explain code.

Swift supports single-line, multi-line (nestable), and documentation comments.

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Single-line and Multi-line

Use // for single-line comments and /* ... */ for multi-line comments.

Example

// This is a single-line comment
print("Hello")

/* This is a
   multi-line comment */
print("Swift")

/* Nested comments are allowed:
  /* inner */
*/

This example shows single- and multi-line comments.

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Documentation Comments

Use /// before declarations to generate documentation, e.g. for functions, types, and properties.

Documentation comments can include parameters, return values, and more.

They differ from regular comments in that they are processed by the compiler and can be used to generate documentation.

Example

/// Returns the sum of two integers.
/// - Parameters: a, b
func add(_ a: Int, _ b: Int) -> Int { a + b }
print(add(2, 3))

This example uses triple-slash comments to document a function.

Swift Number Output

Print numeric values with print() and format using interpolation or format styles.

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Printing Numbers

Print values directly or embed them using string interpolation with \(value).

Example

let a = 7, b = 3
print(a, b)                 // space-separated by default
print("a=\(a), b=\(b)")     // interpolation
print("sum = \(a + b)")     // inline math

This example prints numbers directly and via string interpolation, including inline addition.

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Math Functions

Common functions like abs, min, and max help compute numeric results.

• abs(x) returns the absolute value of x.
• min(x, y) returns the smaller of x and y.
• max(x, y) returns the larger of x and y.

Example

let x = -7
print(abs(x))          // 7
print(min(3, 8))       // 3
print(max(3, 8))       // 8

This example shows absolute value, minimum, and maximum functions.

Use print() to write text and values to output.

Use string interpolation to combine values.

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Print Text

Use print() to write text.

Interpolate values with \(expr).

Example

print("Hello, Swift!")
let name = "Kai"
print("Hello, \(name)!")

let a = 2, b = 3
print("Total: \(a + b)")

This example prints text and uses string interpolation to include values.

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Print Without Newline

Use the terminator parameter to avoid a trailing newline.

Example

for n in 1...3 {
  print(n, terminator: " ") // prints on one line
}
print("done")

This example prints numbers on a single line by setting terminator to a space, then prints done on the next line.