Category: 01. Basic

Swift Arithmetic Operators

Use +, -, *, and / to add, subtract, multiply and divide.

Integer division truncates toward zero.

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Examples

These examples show addition, subtraction, multiplication and integer division.

Example

let a = 7, b = 3
print(a - b)
print(a * b)
print(a / b)        // integer division

This example demonstrates arithmetic with integers.

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Remainder Operator

The remainder operator % gives the leftover after integer division.

Example

print(7 % 3)   // 1
print(8 % 2)   // 0
print(10 % 6)  // 4

Use % to check divisibility or cycle through a fixed range.

Swift Operators

Operators perform operations on values.

Common groups are arithmetic, assignment, comparison and logical operators.

Swift also has well-defined precedence.

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Operator families at a glance

Explore arithmetic, assignment, comparison, and logical operators, and how precedence affects evaluation order.

Example

let a = 5, b = 2
// Arithmetic
print(a + b)
// Comparison
print(a > b)
// Logical
let t = true, f = false
print(t && !f)

This example shows arithmetic (+), comparison (>) and logical (&&, !) operators.

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Unary and Ternary

Unary operators act on a single operand (like ! to negate a boolean).

The ternary conditional operator condition ? a : b chooses between two values.

Example

let flag = false
print(!flag)              // unary NOT
let score = 85
let label = (score >= 90) ? "A" : "Not A"
print(label)

This example flips a boolean with unary ! and uses the ternary operator to pick a string based on a condition.

Swift Type Casting

Use as, as?, and as! to convert between types, especially with protocols and Any.

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Upcasting and Downcasting

Convert a value to a supertype (upcast) or attempt to convert back to a subtype using optional downcasting with as?.

Example

let items: [Any] = [1, "Swift"]
for item in items {
  if let i = item as? Int {
print("Int: \(i)")
  } else if let s = item as? String {
print("String: \(s)")
  }
}

This example conditionally casts values from Any to their concrete types.

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Forced Downcast

Use as! only when you are certain of the runtime type. If the cast fails, the program will crash.

Example

let value: Any = 42
let i = value as! Int   // forced downcast
print(i)

Prefer optional casting (as?) when the type may vary, and unwrap safely.

Swift Characters

Character is one user-visible character.

Strings are collections of characters.

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Characters and String Length

Use Character for single letters.

Use String.count to get the number of characters.

Example

let ch: Character = "A"
print(ch)
let word = "Swift"
print(word.count)

This prints a character and a string length.

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Characters and String Conversion

Convert between Character and String as needed.

Example

let ch: Character = "A"
let s = String(ch)
print(s)              // "A"

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Unicode and Grapheme Clusters

Some characters use multiple Unicode scalars but still count as one character.

Example

let heart: Character = "❤️"
print(heart)
let flag: Character = "🇳🇴" // composed of two regional indicators
print(flag)
print("e\u{301}".count) // 1 (e + combining acute accent)

Swift Booleans

Bool represents logical true/false. Combine conditions with &&, ||, and negate with !.

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Boolean Logic

Combine boolean values using logical AND (&&), OR (||), and negate with NOT (!).

Example

let a = true, b = false
print(a && b)
print(a || b)
print(!a)

This example shows logical AND, OR and NOT.

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Comparison Results

Relational operators like >, ==, and != return Bool values that you can use in conditions.

Example

let a = 5, b = 3
print(a > b)   // true
print(a == b)  // false
print(a != b)  // true

Comparisons like >, ==, and != produce Bool values you can combine with logical operators.

Swift Numbers

Swift has integer types (like Int) and floating-point types (like Double).

Use arithmetic operators to add, subtract, multiply and divide numbers.

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Arithmetic

Use +, -, *, and / to perform numeric operations. Convert types when needed.

Example

let a = 5, b = 2
print(a - b)
print(a * b)
print(Double(a) / Double(b))

This example demonstrates basic arithmetic and integer-to-double conversion for division.

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Integer Division vs Remainder

Integer division drops any fractional part, while % returns the remainder.

Example

let a = 7, b = 3
print(a / b)  // 2 (integer division)
print(a % b)  // 1 (remainder)

This example shows how integer division truncates toward zero and how the remainder operator % returns the leftover.

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.