Swift: Swiftの入出力とデバッグ：print、アサーション、ブレークポイント

let scores = [85, 92, 78, 90, 88]
var total = 0
for i in 0...5 {
    total += scores[i]
}
let average = total / 5
print("Average: \(average)")

let scores = [85, 92, 78, 90, 88]
print("Array length: \(scores.count)")     // Output: 5
var total = 0
for i in 0..<scores.count {               // Use count instead of hardcoding
    print("Processing index \(i): value = \(scores[i])")
    total += scores[i]
}
print("Total: \(total)")
let average = total / 5
print("Average: \(average)")

// Default: space-separated, newline-terminated
print("Hello", "Swift", "World")
// Hello Swift World
// Custom separator
print("Hello", "Swift", "World", separator: ", ")
// Hello, Swift, World
// Custom terminator (no newline)
print("Loading", terminator: "...")
print("Done")
// Loading...Done
// Combined usage
print("A", "B", "C", separator: " | ", terminator: ".\n")
// A | B | C.

let name = "Alice"
let numbers = [1, 2, 3]
print(name)          // Alice
debugPrint(name)     // "Alice"
dump(name)           // - "Alice"
print(numbers)       // [1, 2, 3]
debugPrint(numbers)  // [1, 2, 3]
dump(numbers)
// ▿ 3 elements
//   - 0 : 1
//   - 1 : 2
//   - 2 : 3

// ============================================
// Simulate system log output
// Demonstrates advanced print parameters and debugPrint
// ============================================
let event = "USER_LOGIN"
let user = "Alice"
let statusCode = 200
let duration = 0.045
// 1. Use separator to format the log
print("[\(event)]", user, "Status: \(statusCode)", separator: " | ", terminator: "")
print(" (\(duration)s)")
// [USER_LOGIN] | Alice | Status: 200 (0.045s)
// 2. Output tabular data
print()
print("=== Report ===")
print("Item", "Price", "Qty", separator: " | ")
print("-----", "-----", "---", separator: " | ")
print("Book", "12.99", "3", separator: " | ")
print("Pen", "1.50", "10", separator: " | ")
print("Bag", "49.99", "1", separator: " | ")
// 3. debugPrint for development debugging
let input: String? = "test"
debugPrint("Debug: input = \(input)")
// "Debug: input = Optional(\"test\")"

func calculateDiscount(price: Double, percent: Double) -> Double {
    assert(price > 0, "Price must be greater than 0")
    assert(percent >= 0 && percent <= 100, "Discount must be between 0-100")
    let discount = price * percent / 100.0
    return price - discount
}
let finalPrice = calculateDiscount(price: 100.0, percent: 20)
print(finalPrice)  // 80.0
// The following would trigger assertion failures in Debug mode:
// calculateDiscount(price: -10, percent: 20)  // ❌ assert fails
// calculateDiscount(price: 100, percent: 150) // ❌ assert fails

func sendEmail(to address: String, message: String) {
    precondition(address.contains("@"), "Invalid email address: \(address)")
    precondition(!message.isEmpty, "Message cannot be empty")
    print("Sending email to \(address): \(message)")
}
sendEmail(to: "alice@example.com", message: "Hello!")
// Sending email to alice@example.com: Hello!
// The following would trigger precondition failures (all modes):
// sendEmail(to: "invalid", message: "Hi")

// ============================================
// User registration parameter checks
// Demonstrates assert and precondition usage
// ============================================
import Foundation
func registerUser(name: String, age: Int, email: String) {
    // precondition: Public API contract (active in all modes)
    precondition(name.count >= 2, "Username must be at least 2 characters")
    precondition(age >= 18, "User must be at least 18 years old")
    precondition(email.contains("@"), "Invalid email format")
    // assert: Internal logic check (Debug only)
    let emailParts = email.split(separator: "@")
    assert(emailParts.count == 2, "Email should contain exactly one @ symbol")
    let domain = String(emailParts[1])
    assert(domain.contains("."), "Email domain is invalid")
    // Actual registration logic
    print("Registration successful: \(name), age \(age)")
    print("Confirmation email sent to: \(email)")
}
// Valid call
registerUser(name: "Alice", age: 28, email: "alice@example.com")
print("---")
// Calls that would trigger precondition failures (commented out to avoid crashing)
// registerUser(name: "A", age: 20, email: "test@test.com")

// Run in Playground — the sidebar shows each step's result
let name = "Alice"    // "Alice"
var score = 0         // 0
score += 85           // 85
score += 92           // 177
let average = score / 2  // 88

func calculateTotal(items: [Double], tax: Double) -> Double {
    var subtotal = 0.0
    // Set a breakpoint on this line
    for item in items {
        subtotal += item
    }
    let taxAmount = subtotal * tax
    let total = subtotal + taxAmount
    return total
}
let cart = [29.99, 49.99, 15.00]
let final = calculateTotal(items: cart, tax: 0.08)
print("Total: $\(final)")

// ============================================
// Practice Playground debugging techniques
// Paste this code into a Playground and run it
// ============================================
import Foundation
// 1. Set a breakpoint on the line below to observe variable values
let data: [String: Any] = [
    "product": "Swift Book",
    "price": 39.99,
    "quantity": 3,
    "inStock": true
]
// 2. Step through the following code
let productName = data["product"] as? String ?? "Unknown"
let price = data["price"] as? Double ?? 0.0
let quantity = data["quantity"] as? Int ?? 0
let inStock = data["inStock"] as? Bool ?? false
print("Product: \(productName)")
print("Price: $\(price)")
print("Quantity: \(quantity)")
print("In Stock: \(inStock)")
// 3. Observe the conditional check results
if inStock {
    let totalCost = price * Double(quantity)
    print("Total Cost: $\(totalCost)")
} else {
    print("Item is out of stock")
}
// 4. Use dump to inspect complex data
print("\n=== Debug Info ===")
dump(data)

// ============================================
// Grade analysis tool
// Combines print debugging + assertion checks + formatted output
// ============================================
import Foundation
// 1. Student grade data
let studentName = "Alice"
let scores = [85.0, 92.0, 78.0, 90.0, 88.0]
// 2. Debug assertions to validate data
assert(scores.count > 0, "Score list cannot be empty")
for score in scores {
    assert(score >= 0 && score <= 100, "Score must be between 0-100: \(score)")
}
// 3. Calculate statistics
var total = 0.0
var highest = scores[0]
var lowest = scores[0]
// Set a breakpoint here to observe the loop process
for (index, score) in scores.enumerated() {
    print("[DEBUG] Index \(index): \(score)")
    total += score
    if score > highest { highest = score }
    if score < lowest { lowest = score }
}
let average = total / Double(scores.count)
// 4. Formatted output
print(String(repeating: "=", count: 35))
print("Student: \(studentName)")
print(String(repeating: "-", count: 35))
print("Subject", "Score", "Grade", separator: " | ")
print(String(repeating: "-", count: 35))
for (index, score) in scores.enumerated() {
    let grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 70 ? "C" : "D"
    print("Subject \(index + 1)", score, grade, separator: " | ")
}
print(String(repeating: "-", count: 35))
print("Total: \(total)")
print("Average: \(String(format: "%.1f", average))")
print("Highest: \(highest)")
print("Lowest: \(lowest)")
print(String(repeating: "=", count: 35))
// 5. Precondition to ensure reasonable results
precondition(average >= 0 && average <= 100, "Average is outside expected range")
precondition(highest >= lowest, "Highest score should not be lower than lowest")