Category: 01. Basic

Swift else if

Chain multiple conditions with else if for more than two branches.

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Branch with else if conditions

Use else if for additional conditions when the first if is false.

Example

let score = 72
if score >= 90 {
  print("A")
} else if score >= 80 {
  print("B")
} else if score >= 70 {
  print("C")
} else {
  print("Below C")
}

This example evaluates multiple ranges using chained else if clauses.

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REMOVE ADS

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Temperature Levels

Use multiple else if branches to categorize values.

Example

let t = 0
if t <= 0 {
  print("Freezing")
} else if t < 10 {
  print("Cold")
} else if t < 20 {
  print("Cool")
} else {
  print("Warm")
}

Swift else

Use else to handle the false branch of a condition.

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Handle the false branch with else

Use else to run an alternate block when the condition is false.

Example

let hasAccess = false
if hasAccess {
  print("Welcome")
} else {
  print("Denied")
}

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Age Gate

Use else to handle when a user does not meet a requirement.

Example

let age = 16
if age >= 18 {
  print("Access granted")
} else {
  print("Access denied")
}

Swift if

Execute code conditionally when an expression evaluates to true.

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Basic if

Run code only when a condition evaluates to true.

Example

let temp = 25
if temp > 20 {
  print("Warm")
}

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Threshold Check

Trigger an action only when a value exceeds a threshold.

Example

let speed = 55
if speed > 50 {
  print("Slow down")
}

Swift If…Else

Control the flow of your program with if, else if, and else.

Combine conditions with logical operators.

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Basic If…Else

Use if to run code when a condition is true.

Add else for the false case, and else if for multiple branches.

Example

let score = 82
if score >= 90 {
  print("A")
} else if score >= 80 {
  print("B")
} else {
  print("C or lower")
}

This example prints a letter grade based on the score.

Tip: Swift conditions must be Bool.

There is no implicit conversion from integers to booleans.

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Even or Odd

Use else to handle the alternate outcome.

Example

let n = 7
if n % 2 == 0 {
  print("Even")
} else {
  print("Odd")
}

Swift Ranges

Use ranges to express a sequence of values.

a...b is a closed range including both ends.

a..<b is a half-open range up to but not including b.

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Closed and Half-Open

Use a...b for closed ranges (inclusive) and a..<b for half-open ranges (exclusive upper bound).

Example

for n in 1...5 {
  print(n)
} 
for n in 1..<5 {
  print(n)
}
let r = 10...12
print(r.contains(11))
print(r.contains(13))

This example iterates over closed and half-open ranges and checks membership with contains().

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One-Sided Ranges

One sided ranges omit one end: ...b starts from the beginning, and a... goes to the end.

Example

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

Swift Arrays: Real-Life Examples

Arrays are everywhere: rendering lists, aggregating values, finding items, and transforming data.

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Aggregate and Transform

Use filter, map, and reduce to process arrays declaratively.

Example

let scores = [72, 88, 95, 64, 83]
let passed = scores.filter { $0 >= 75 }
let curved = passed.map { $0 + 5 }
let average = curved.reduce(0, +) / curved.count
print(passed)
print(curved)
print("Average: \(average)")

Filter to keep passing scores, map to apply a curve, then reduce to compute an average.

Tip: Prefer declarative iteration for clarity and fewer bugs.

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Search & Index

Check for membership and find the index of a value.

Example

let names = ["Kai", "Bjorn", "Stale"]
print(names.contains("Bjorn"))            // true
if let i = names.firstIndex(of: "Stale") {
  print(i)                                 // 2
}

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)") }