Author: saqibkhan

Swift Collections

Use arrays, dictionaries, and sets to store ordered lists, key-value pairs, and unique items.

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Arrays

Arrays store ordered lists of values.

Syntax: [Type] for type, append with .append, count with .count, access with array[index].

Example

var nums: [Int] = [1, 2, 3]
nums.append(4)
print(nums.count)    // 4
print(nums[0])       // 1

This example creates an [Int] array, appends a value, reads the count, and accesses the first element.

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Dictionaries

Dictionaries store key-value pairs.

Syntax: [Key: Value] for type, assign with dict[key] = value, read with dict[key] ?? default.

Example

var ages: [String: Int] = ["Kai": 30]
ages["Elisabeth"] = 25
print(ages["Kai"] ?? 0)

This example defines a [String: Int] dictionary, inserts a key, and reads with nil-coalescing.

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Sets

Sets store unique items.

Syntax: Set<Element> or literal, test membership with .contains.

Example

var letters: Set<Character> = ["a", "b", "a"]
print(letters.contains("a"))

Swift Break/Continue

Use break to exit a loop early, and continue to skip to the next iteration.

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break

Stop the loop immediately when a condition is met.

Example

for i in 1...10 {
  if i == 4 { break }
  print(i)
}

This example stops printing when i reaches 4.

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continue

Skip the rest of the current iteration but keep looping.

Example

for i in 1...5 {
  if i % 2 == 0 { continue }
  print(i) // only odd numbers
}

Swift For Loop (Real-Life)

Use loops to process arrays, paginate data, or aggregate results.

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Process arrays and aggregate results

Loop over a collection and accumulate values to compute totals like sums or averages.

Example

let numbers = [1,2,3,4,5]
var sum = 0
for n in numbers { sum += n }
print(sum)

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Filter Even Numbers

Filter a collection to keep only the values you need.

Example

let numbers = [1,2,3,4,5]
let evens = numbers.filter { $0 % 2 == 0 }
print(evens)

Swift For-Each Loop

Use forEach to iterate sequences with a closure.

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Iterate with forEach closures

Pass a closure to forEach to process each element of a sequence.

Example

["A","B","C"].forEach { print($0) }

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Enumerated forEach

Use enumerated() with forEach to get index and value.

Example

let items = ["A","B","C"]
items.enumerated().forEach { print("\($0.offset): \($0.element)") }

Swift Nested Loops

Place a loop inside another loop to generate combinations or matrices.

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Generate combinations with nested loops

Use inner and outer loops to produce pairs or grids from ranges and collections.

Example

for i in 1...2 {
  for j in 1...3 {
print(i, j)
  }
}

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Multiplication Table

Use nested loops to build a small multiplication table.

Example

for i in 1...3 {
  var row = ""
  for j in 1...3 {
row += "\(i*j) "
  }
  print(row)
}

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Swift For Loop

Use for-in to iterate over ranges, arrays, dictionaries, and other sequences.

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Iterate a Range

Use a range to loop a fixed number of times.

Example

for i in 1...3 {
  print(i)
}

This example iterates from 1 to 3 inclusive.

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Iterate an Array

Loop through an array with for-in or enumerated() to access index and value.

Example

let nums = [10, 20, 30]
for n in nums {
  print(n)
}
for (index, value) in nums.enumerated() {
  print("index: \(index), value: \(value)")
}

Use enumerated() to get index and value together.

Swift While (Real-Life Examples)

Use loops to retry operations, poll statuses, or process queues carefully with exit conditions.

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While Loop from 3 to 1

Count down from 3 to 1.

Example

var remaining = 3
while remaining > 0 {
  print("Remaining: \(remaining)")
  remaining -= 1
}

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Poll Until Success

Repeat an action with a cap on attempts until a condition is met.

Example

var attempts = 0
var success = false
while !success && attempts < 5 {
  attempts += 1
  print("Checking... #\(attempts)")
  if attempts == 3 {
success = true
print("Success!")
  }
}

Swift Repeat/While Loop

Use repeat { ... } while condition to run the body at least once.

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Repeat/while Loop Example

This example uses a repeat/while loop to print “Try #1” and “Try #2”.

Example

var attempts = 0
repeat {
  attempts += 1
  print("Attempt #\(attempts)")
} while attempts < 3

This example demonstrates repeat (do-while style).

Tip: Avoid infinite loops. Ensure the loop condition will eventually become false.

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REMOVE ADS

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Runs Once Even If Condition Is False

Because repeat checks the condition after the body, it executes at least once.

Example

var n = 0
repeat {
  print("Runs once")
} while n > 0

Repeat code while a condition is true using while.

Use repeat { ... } while to check the condition after the loop body.

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while

The while loop checks the condition before each iteration.

Example

var n = 3
while n > 0 {
  print(n)
  n -= 1
}
print("Liftoff!")

This example counts down from 3 using a while loop.

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repeat { } while

repeat runs the body first, then checks the condition.

Example

var attempts = 0
repeat {
  attempts += 1
  print("Attempt #\(attempts)")
} while attempts < 3

This example demonstrates repeat (do-while style).

Swift Switch

Use switch to match a value against patterns.

In Swift, a switch must list every choice, and it stops checking more choices after the first match.

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Basic Switch

Match integer ranges and exact values.

Add default to handle remaining cases.

Example

let grade = 82
switch grade {
case 90...100:
  print("A")
case 80..<90:
  print("B")
case 70..<80:
  print("C")
default:
  print("Below C")
}

This example categorizes a score using ranges in switch.

Note: Swift switch must be exhaustive. Use default to cover remaining cases.

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String Switch

Switch can match strings directly against literal cases.

Example

let command = "start"
switch command {
case "start":
  print("Starting")
case "stop":
  print("Stopping")
default:
  print("Unknown")
}