Control Flow 🔀

// if / else if / else — your program makes a decision.
// Swift needs NO parentheses around the test, but braces { } are ALWAYS required.
let temperature = 28
print("temperature = \(temperature)")

if temperature > 35 {
    print("🔥 Extremely hot — stay hydrated.")
} else if temperature > 25 {
    print("☀️ Warm — perfect for the beach!")   // 28 > 25, so THIS line runs
} else if temperature > 15 {
    print("🌤️ Mild — grab a light jacket.")
} else {
    print("🧥 Cold — wear a coat.")
}

// A condition is anything that evaluates to a Bool (true / false).
let age = 20
let canVote = age >= 18            // >= means "greater than or equal to" → true
print("canVote = \(canVote)")

// Combine conditions with && (AND), || (OR), ! (NOT).
let isWeekend = true
let isSunny = false
print("beach day? \(isWeekend && isSunny)")   // both must be true → false
print("relax day? \(isWeekend || isSunny)")   // either is enough  → true

// Ternary operator: condition ? valueIfTrue : valueIfFalse
let label = age >= 18 ? "Adult" : "Minor"
print("label = \(label)")

temperature = 28
☀️ Warm — perfect for the beach!
canVote = true
beach day? false
relax day? true
label = Adult

// 🎯 YOUR TURN — replace each ___ then run it on SwiftFiddle.

let score = 72

// 1) Print "Pass" if score is 50 or more, otherwise "Fail".
//    Fill in the condition (use >= for "greater than or equal to").
if score ___ 50 {            // 👉 replace ___ with the >= operator
    print("Pass")
} else {
    print("Fail")
}

// 2) Set message to "Adult" when age is 18+, else "Minor", using a ternary.
let age = 16
let message = age >= 18 ? ___ : ___   // 👉 two strings in "double quotes"
print(message)

// ✅ Expected output:
//    Pass
//    Minor

Pass
Minor

// Swift's switch is exhaustive (must cover every case) and has
// NO implicit fallthrough — only the matching case runs, no break needed.

// (a) Match several values in one case.
let day = "Wednesday"
switch day {
case "Saturday", "Sunday":
    print("🎉 Weekend — relax!")
case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
    print("📅 Weekday — time to work!")   // Wednesday matches here
default:
    print("❓ Unknown day")               // default makes it exhaustive
}

// (b) Match RANGES. 1...5 is closed (incl. 5); 1..<5 is half-open (excl. 5).
let scoreValue = 85
let grade: String
switch scoreValue {
case 90...100: grade = "A"
case 80..<90:  grade = "B"     // 80 up to but NOT including 90 → 85 lands here
case 70..<80:  grade = "C"
default:       grade = "F"
}
print("Score \(scoreValue) → Grade \(grade)")

// (c) Match TUPLES, bind values with let, and refine with where.
let point = (2, 4)
switch point {
case (0, 0):
    print("At the origin")
case (let x, 0):
    print("On the x-axis at \(x)")        // value binding: capture x
case (let x, let y) where x == y:
    print("On the diagonal")
case (let x, let y):
    print("Somewhere at (\(x), \(y))")    // binds both coordinates
}

📅 Weekday — time to work!
Score 85 → Grade B
Somewhere at (2, 4)

// 🎯 YOUR TURN — finish the grade switch by filling in the ranges.

let mark = 64
let grade: String

switch mark {
case 70...100: grade = "Distinction"
case ___:      grade = "Merit"        // 👉 60 up to (not incl.) 70  → 60..<70
case 50..<60:  grade = "Pass"
___:           grade = "Fail"         // 👉 the catch-all keyword that makes it exhaustive
}

print("Mark \(mark) → \(grade)")

// ✅ Expected output:
//    Mark 64 → Merit

Mark 64 → Merit

// for-in over a CLOSED range (1 through 5 inclusive).
for i in 1...5 {
    print("\(i) squared = \(i * i)")
}

// for-in over an ARRAY.
let fruits = ["Apple", "Banana", "Cherry"]
for fruit in fruits {
    print("🍎 \(fruit)")
}

// enumerated() gives (index, value) pairs.
for (index, fruit) in fruits.enumerated() {
    print("\(index): \(fruit)")
}

// while — checks the condition BEFORE each pass (may run zero times).
var countdown = 3
while countdown > 0 {
    print("\(countdown)...")
    countdown -= 1
}

// repeat-while — runs the body FIRST, then checks. Always runs at least once.
var attempts = 0
repeat {
    attempts += 1
    print("attempt \(attempts)")
} while attempts < 2

print("🚀 Liftoff!")

1 squared = 1
2 squared = 4
3 squared = 9
4 squared = 16
5 squared = 25
🍎 Apple
🍎 Banana
🍎 Cherry
0: Apple
1: Banana
2: Cherry
3...
2...
1...
attempt 1
attempt 2
🚀 Liftoff!

// An OPTIONAL may hold a value OR nothing (nil). Its type ends with ?.
// You must safely unwrap it before using the value.

let input = "42"

// if let — runs the block ONLY if the conversion succeeds (binds 'number').
if let number = Int(input) {
    print("Parsed \(number)")        // Int("42") succeeds → 42
} else {
    print("Not a number")
}

// guard let — the "early exit". If unwrapping fails, you MUST leave the scope.
// The unwrapped value then stays available for the REST of the function.
func greet(_ name: String?) {
    guard let name = name else {
        print("No name given")        // guard's else must exit (return here)
        return
    }
    print("Hello, \(name)!")          // 'name' is a real String from here on
}

greet("Ada")
greet(nil)

// guard also works on plain conditions — fail fast, keep the happy path flat.
func checkAge(_ age: Int) {
    guard age >= 18 else {
        print("Too young")
        return
    }
    print("Welcome!")
}

checkAge(20)
checkAge(15)

Parsed 42
Hello, Ada!
No name given
Welcome!
Too young