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Arrays and Loops

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An array stores an ordered collection of values of the same data type.

Use the initializer syntax, [Type](), to create an empty array of a certain type.

var scores = [Int]() // The array is empty: []

Initialize with Array Literal

An array can be initialized with an array literal, which is a short-hand method of writing one or more values as an array collection.

An array literal is written as a list of values, separated by commas, and surrounded by a pair of square brackets.

// Using type inference: var snowfall = [2.4, 3.6, 3.4, 1.8, 0.0] // Being explicit with the type: var temp: [Int] = [33, 31, 30, 38, 44]


An index refers to an item’s position within an ordered list. Use the subscript syntax, array[index], to retrieve an individual element from an array.

Note: Swift arrays are zero-indexed, meaning the first element has index 0.

var vowels = ["a", "e", "i", "o", "u"] print(vowels[0]) // Prints: a print(vowels[1]) // Prints: e print(vowels[2]) // Prints: i print(vowels[3]) // Prints: o print(vowels[4]) // Prints: u

.count Property

The .count property returns the number of elements in an array.

var grocery = ["πŸ₯“", "πŸ₯ž", "πŸͺ", "πŸ₯›", "🍊"] print(grocery.count) // Prints: 5

.append() Method and += Operator

The .append() method can be called on an array to add an item to the end of the array.

The += addition assignment operator can be used to add the elements of another array to the existing array.

var gymBadges = ["Boulder", "Cascade"] gymBadges.append("Thunder") gymBadges += ["Rainbow", "Soul"] // ["Boulder", "Cascade", "Thunder", "Rainbow", "Soul"]

.insert() and .remove() Methods

The .insert() method can be called on an array to add an element at a specified index. It takes two arguments: value and at: index.

The .remove() method can be called on an array to remove an element at a specified index. It takes one argument: at: index.

var moon = ["πŸŒ–", "πŸŒ—", "🌘", "πŸŒ‘"] moon.insert("πŸŒ•", at: 0) // ["πŸŒ•", "πŸŒ–", "πŸŒ—", "🌘", "πŸŒ‘"] moon.remove(at: 4) // ["πŸŒ•", "πŸŒ–", "πŸŒ—", "🌘"]

Iterating Over an Array

In Swift, a for-in loop can be used to iterate through the items of an array.

This is a powerful tool for working with and manipulating a large amount of data.

var employees = ["Michael", "Dwight", "Jim", "Pam", "Andy"] for person in employees { print(person) } // Prints: Michael // Prints: Dwight // Prints: Jim // Prints: Pam // Prints: Andy


Ranges created by the ... operator will include the numbers from the lower bound to (and includes) the upper bound.

let zeroToThree = 0...3 // zeroToThree: 0, 1, 2, 3

stride() Function

Calling stride() with the 3 necessary arguments creates a collection of numbers; the arguments decide the starting number to, the (excluded) ending number, and how to increment/decrement from the start to the end.

for oddNum in stride(from: 1, to: 5, by: 2) { print(oddNum) } // Prints: 1 // Prints: 3

for-in Loop

The for-in loop is used to iterate over collections, including strings and ranges.

for char in "hehe" { print(char) } // Prints: h // Prints: e // Prints: h // Prints: e

continue Keyword

The continue keyword will force the loop to move on to the next iteration.

for num in 0...5 { if num % 2 == 0 { continue } print(num) } // Prints: 1 // Prints: 3 // Prints: 5

break Keyword

To terminate a loop before its completion, use the break keyword.

for char in "supercalifragilisticexpialidocious" { if char == "c" { break } print(char) } // Prints: s // Prints: u // Prints: p // Prints: e // Prints: r

Using Underscore

Use _ instead of a placeholder variable if the variable is not referenced in the for-in loop body.

for _ in 1...3 { print("OlΓ©") } // Prints: OlΓ© // Prints: OlΓ© // Prints: OlΓ©

while Loop

A while loop accepts a condition and continually executes its body’s code for as long as the provided condition is true.

If the condition is never false then the loop continues to run and the program is stuck in an infinite loop.

var counter = 1 var stopNum = Int.random(in: 1...10) while counter < stopNum { print(counter) counter += 1 } // The loop prints until the stop condition is met

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