Author: saqibkhan

Swift Arrays: Multidimensional

Use nested arrays to represent 2D (or higher) structures such as matrices and grids.

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2D Arrays

Store rows as arrays inside an outer array, then index as grid[row][col] to access items.

Example

var grid = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]
print(grid[0][1]) // 2
for row in grid {
  print(row)
}

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Update a Cell

Change a value by indexing into the specific row and column.

Example

var grid = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]
grid[1][1] = 99
print(grid[1])      // [4, 99, 6]
print(grid[1][1])   // 99

Swift Arrays: Indices & Bounds

Arrays have startIndex and endIndex (one past last).

Use indices to loop valid positions.

Out-of-bounds access crashes at runtime.

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Valid Indices

Use indices to visit only valid positions.

Example

let items = [10, 20, 30]
print(items.startIndex)       // 0
for i in items.indices {
  print("index: \(i), value: \(items[i])")
}

Valid subscript indices: 0..<items.count (zero up to, not including, count).

Example

let items = [10, 20, 30]
print(items[0])   // OK
// print(items[3]) // out of bounds

Use indices for index-and-value access without enumerated().

Note: endIndex is not a valid subscript. The last valid index is items.index(before: items.endIndex).

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Last Valid Index

Get the last valid index with index(before: endIndex).

Example

let items = [10, 20, 30]
let lastIndex = items.index(before: items.endIndex)
print(lastIndex)        // 2
print(items[lastIndex]) // 30

Swift Arrays: Slices

Use ranges to create slices of arrays.

A range is a half-open interval, meaning it includes the lower bound but excludes the upper bound.

A slice is a view of an array that shares storage with the base array, meaning it is a reference to a portion of the array.

When you modify a slice, the base array is also modified.

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ArraySlice

Create an ArraySlice with a range on an array.

Convert to Array if you need its own storage.

Example

let nums = [10, 20, 30, 40, 50]
let middle = nums[1...3]          // ArraySlice<Int>
print(middle)                     // [20, 30, 40]
let copy = Array(middle)          // Array<Int>
print(copy)

Use a half-open range to exclude the upper bound:

Example

let nums = [10, 20, 30, 40, 50]
let slice = nums[1..<3]   // indices 1 and 2
print(slice)               // [20, 30]

Slices share storage with the base array until you copy.

Tip: Slices keep original indices.

Convert to Array for zero-based indices.

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One-Sided Slices

Use one-sided ranges to slice from the start or to the end.

Example

let arr = [0, 1, 2, 3, 4]
print(arr[...2])  // first three elements (0...2)
print(arr[2...])  // from index 2 to the end

Swift Arrays: Loop

Use for-in to loop values.

Use enumerated() for index and value.

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Loop Elements

Loop values with for-in, or use enumerated() for index and value.

Example

let fruits = ["Apple", "Banana", "Cherry"]
for fruit in fruits {
  print(fruit)
}
for (i, fruit) in fruits.enumerated() {
  print("\(i): \(fruit)")
}

Get index and value with enumerated().

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forEach

Use forEach for a functional style loop. It reads values but cannot use break/continue.

Example

let fruits = ["Apple", "Banana", "Cherry"]
fruits.forEach { print($0) }
fruits.enumerated().forEach { print("\($0.offset): \($0.element)") }

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())