Category: 01. Basic

Swift Arrays

Arrays store ordered collections of values of the same type.

Arrays are value types and copy on write.

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Create and Access

Create arrays with literals or initializers.

Access elements by index and use properties like count and isEmpty.

Example

var numbers = [10, 20, 30]
print(numbers[0])         // 10
numbers.append(40)
print(numbers.count)      // 4
print(numbers.isEmpty)    // false

This example creates an array, accesses items, appends, and inspects properties.

Tip: Arrays are value types.

Mutating a copy will not affect the original (copy-on-write semantics).

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Insert and Remove

Modify arrays by inserting and removing elements.

Example

var items = ["A", "B", "C"]
items.insert("X", at: 1)
print(items)
items.remove(at: 2)
print(items)

Swift strings are Unicode-correct.

A single character can be composed of multiple Unicode scalars.

Visually identical strings can compare equal.

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Composed Characters

Some characters are made from multiple Unicode scalars; Swift treats them as a single character for comparison and length.

Example

let e1 = "é"
let e2 = "e\u{301}"   // e + COMBINING ACUTE ACCENT
print(e1 == e2)
print(e2)

This example shows that a precomposed character and a composed sequence are considered equal in Swift.

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Unicode Scalars

Inspect the underlying Unicode scalar values with the unicodeScalars view.

The unicodeScalars view yields values of type UnicodeScalar.

Example

let s = "e\u{301}"
for scalar in s.unicodeScalars {
  print(scalar.value)   // 101, 769
}

Use escape sequences inside strings: \n (newline), \t (tab), \" (quote), \\ (backslash).

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Escapes

Escape special characters with backslashes to represent newlines, tabs, quotes, or backslashes themselves.

Example

print("Hello\nSwift")
print("A\tB\tC")
print("\"quoted\"")
print("\\")

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Multiline Strings

Use triple quotes """ for multiline string literals. Indentation before closing quotes is ignored.

Example

let poem = """
Roses are red,
Violets are blue.
"""
print(poem)

Swift Strings: Numbers and Strings

Use string interpolation to mix numbers with text.

Convert numbers to strings explicitly with String(value) when concatenating.

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Mix Text and Numbers

Use interpolation to embed numbers directly in strings, or convert numbers with String(value) when concatenating.

Example

let age = 5
print("Age: \(age)")          // interpolation
let text = "You are " + String(age)
print(text)
let pi = 3.14
print("pi = \(pi)")

This example shows interpolation and explicit conversion with String().

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Convert String to Number

Use numeric initializers like Int("123") which return optionals because conversion can fail.

Example

let s1 = "123"
let n1 = Int(s1)           // Int?
print(n1 ?? 0)

let s2 = "abc"
let n2 = Int(s2)           // nil (not a number)
print(n2 == nil)

Join strings with +, or use interpolation to insert values into a string.

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Concatenate vs Interpolate

Use + to make a new string. Use interpolation to insert values inline.

Example

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

Interpolation is often clearer when mixing text and values.

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Append Strings

Use += to append to a mutable string.

Example

var s = "Hello"
s += ", Swift"
print(s)

Strings are text. Use + to join, interpolation with \(value) to insert values, and properties like count and isEmpty to inspect them.

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Basics

Create, combine, and inspect strings with concatenation, interpolation, and common properties.

Example

let s1 = "Hello"
let s2 = "Swift"
print(s1 + " " + s2)
print("\(s1), \(s2)!")
let word = "Swift"
print(word.count)
print(s1.isEmpty)

This example shows concatenation, interpolation, count, and isEmpty.

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Substring and Case

Get substrings with indices. Uppercased/lowercased creates new strings without changing the original.

Example

let text = "Swift"
let start = text.startIndex
let end = text.index(start, offsetBy: 3)
let sub = text[start..<end]  // "Swi"
print(sub)
print(text.uppercased())

Swift Operator Precedence

Operator precedence determines evaluation order.

Multiplication comes before addition; && before ||.

Use parentheses to control order.

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Control order of evaluation with precedence

Understand how operators are prioritized and add parentheses to make evaluation order explicit when needed.

Example

print(2 + 3 * 4)
print((2 + 3) * 4)
print(true || false && false)
print((true || false) && false)

This example shows how parentheses change the result.

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Boolean Precedence

&& is evaluated before ||. Use parentheses to clarify intention.

Example

let a = true
let b = false
let c = true

print(a || b && c)         // true (&& before ||)
print((a || b) && c)       // true
print(a && b || c)         // true ((a && b) || c)

Swift Logical Operators

Combine booleans with && (AND), || (OR), and ! (NOT).

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Logical AND (&&)

Both must be true for the result to be true.

Example

let isOwner = true
let isAdmin = false
print(isOwner && isAdmin)
print(true && true)

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Logical OR (||)

At least one true makes the result true.

Example

let a = true
let b = false
print(a || b)
print(false || false)

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Logical NOT (!)

Flip a boolean value: true becomes false and vice versa.

Example

let flag = false
print(!flag)
print(!true)

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Swift Comparison Operators

Use comparison operators to compare values: ==, !=, >, <, >=, <=.

They return Bool.

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Compare Integers

Use ==, !=, >, <, >=, and <= to compare numeric values.

The result is a Bool.

Example

let a = 5, b = 2
print(a == b)
print(a != b)
print(a > b)
print(a < b)
print(a >= 5)

This example prints the result of several comparisons.

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Compare Strings

Strings compare lexicographically (dictionary order).

Comparison is case-sensitive.

Example

print("apple" < "banana")  // true
print("Swift" == "Swift")  // true
print("cat" > "car")       // true

This example compares strings using the same operators.

Swift Assignment Operators

Use = to assign a value.

Compound assignment operators like +=, -=, *= and /= update a variable in place.

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Compound Assignment

Use compound operators like += and *= to update a variable in place.

Example

var total = 10
total += 5
print(total)
total -= 3
print(total)
total *= 2
print(total)
total /= 4
print(total)

This example shows updating a variable with compound assignment operators.

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Append to String

You can also use += with strings to append text to a mutable string variable.

Example

var s = "Hello"
s += ", Swift"
print(s)

This example appends to a string in place with +=.