Swift For-In Loop

Iterate through collections and sequences efficiently

🔄 What is For-In Loop?

Swift for-in loops iterate through sequences like arrays, ranges, and strings. They provide a clean, readable way to process each element in a collection without manual index management. 


// Basic for-in loop
let colors = ["red", "green", "blue"]
for color in colors {
    print("Color: \(color)")
}

Output:

Color: red

Color: green

Color: blue

For-In Loop Variations

📊

Array Iteration

Loop through array elements 

for item in array {
    print(item)
}
🔢

Range Iteration

Loop through number ranges 

for i in 1...5 {
    print(i)
}
📝

String Iteration

Loop through string characters 

for char in "Hello" {
    print(char)
}
🗂️

Dictionary Iteration

Loop through key-value pairs 

for (key, value) in dict {
    print("\(key): \(value)")
}

🔹 Iterating Through Arrays

The most common use of for-in loops: 

let animals = ["🐶", "🐱", "🐰", "🐸"]

for animal in animals {
    print("Animal: \(animal)")
}

// With enumerated() to get index
for (index, animal) in animals.enumerated() {
    print("\(index + 1). \(animal)")
}

Output:

Animal: 🐶

Animal: 🐱

Animal: 🐰

Animal: 🐸

1. 🐶

2. 🐱

3. 🐰

4. 🐸

🔹 Range-Based Loops

Use ranges to create numeric sequences: 

// Closed range (includes both ends)
for i in 1...5 {
    print("Closed range: \(i)")
}

// Half-open range (excludes upper bound)
for i in 1..<5 {
    print("Half-open range: \(i)")
}

// Reverse order
for i in (1...5).reversed() {
    print("Reverse: \(i)")
}

Output:

Closed range: 1, 2, 3, 4, 5

Half-open range: 1, 2, 3, 4

Reverse: 5, 4, 3, 2, 1

🔹 Dictionary Iteration

Loop through dictionaries to access keys and values: 

let scores = ["Alice": 95, "Bob": 87, "Carol": 92]

// Iterate through key-value pairs
for (name, score) in scores {
    print("\(name) scored \(score)")
}

// Iterate through keys only
for name in scores.keys {
    print("Student: \(name)")
}

// Iterate through values only
for score in scores.values {
    print("Score: \(score)")
}

Output:

Alice scored 95

Bob scored 87

Carol scored 92

Student: Alice, Bob, Carol

Score: 95, 87, 92

🔹 String Character Iteration

Process each character in a string: 

let word = "Swift"

for character in word {
    print("Character: \(character)")
}

// Count vowels example
let text = "Hello World"
var vowelCount = 0

for char in text.lowercased() {
    if "aeiou".contains(char) {
        vowelCount += 1
    }
}
print("Vowels found: \(vowelCount)")

Output:

Character: S, w, i, f, t

Vowels found: 3

🧠 Test Your Knowledge

What's the difference between 1...5 and 1..<5?