Swift: Swiftのループ：for-in、while、repeat-while

// The pain: manual line-by-line processing
let logEntry1 = "2026-07-15 10:23:45 [ERROR] DB timeout"
let logEntry2 = "2026-07-15 10:24:01 [INFO] Request completed"
// ... 99,998 more lines to go

let logEntries = [
    "2026-07-15 10:23:45 [ERROR] DB timeout",
    "2026-07-15 10:24:01 [INFO] Request completed",
    "2026-07-15 10:25:30 [ERROR] Connection refused"
]
var errorCount = 0
for entry in logEntries {
    if entry.contains("[ERROR]") {
        errorCount += 1
    }
}
print("Found \(errorCount) errors in log")

// Traverse an array
let fruits = ["apple", "banana", "orange"]
for fruit in fruits {
    print("I like \(fruit)")
}
// Traverse a range
for number in 1...5 {
    print("Count: \(number)")
}
// Indexed traversal
let colors = ["red", "green", "blue"]
for (index, color) in colors.enumerated() {
    print("\(index + 1). \(color)")
}

let scores = ["Alice": 95, "Bob": 82, "Charlie": 78]
for (name, score) in scores {
    print("\(name): \(score)")
}

// ============================================
// Calculate average from temperature data using for-in
// ============================================
let monthlyTemps = [5.2, 8.1, 12.5, 18.3, 24.1, 30.2,
                    32.0, 31.5, 27.8, 21.3, 14.2, 8.9]
var total = 0.0
for temp in monthlyTemps {
    total += temp
}
let average = total / Double(monthlyTemps.count)
print("Total: \(total) C")
print("Average: \(String(format: "%.1f", average)) C")

var countdown = 5
while countdown > 0 {
    print("\(countdown)...")
    countdown -= 1
}
print("Liftoff!")

var attempts = 0
var success = false
repeat {
    attempts += 1
    print("Attempt #\(attempts)...")
    success = Int.random(in: 1...10) > 5
} while !success && attempts < 3
print(success ? "Succeeded!" : "Failed after 3 attempts")

// ============================================
// Number guessing game with repeat-while
// ============================================
import Foundation
let target = Int.random(in: 1...20)
var guess = 0
var attempts = 0
print("Guess a number between 1 and 20")
repeat {
    attempts += 1
    guess = Int.random(in: 1...20)
    print("Attempt \(attempts): guessed \(guess)")
    if guess < target {
        print("  Too low")
    } else if guess > target {
        print("  Too high")
    } else {
        print("  Correct!")
    }
} while guess != target
print("Solved in \(attempts) attempts!")

let numbers = [3, 7, 1, 9, 4, 6, 8]
// break: exit when first even number found
for num in numbers {
    if num.isMultiple(of: 2) {
        print("Found first even: \(num)")
        break
    }
}
// continue: only print odd numbers
for num in numbers {
    if num.isMultiple(of: 2) {
        continue
    }
    print("Odd: \(num)")
}

// Breaking out of multiple loops with a label
outerLoop: for i in 1...5 {
    for j in 1...5 {
        let product = i * j
        if product == 12 {
            print("Found: \(i) x \(j) = \(product)")
            break outerLoop
        }
    }
}

// ============================================
// Processing log data with break/continue
// ============================================
let logEntries = [
    "INFO Server started",
    "ERROR Database connection failed",
    "DEBUG Cache hit ratio 85%",
    "ERROR Timeout after 30s",
    "INFO Request completed in 120ms",
    "ERROR Disk space low"
]
var errorCount = 0
for entry in logEntries {
    if entry.hasPrefix("DEBUG") {
        continue
    }
    if entry.hasPrefix("ERROR") {
        errorCount += 1
        print("[ERROR #\(errorCount)] \(entry)")
    }
    if errorCount >= 5 {
        print("ALERT: Too many errors!")
        break
    }
}
print("Processed \(logEntries.count) entries, found \(errorCount) errors")

// ============================================
// Log analysis tool
// Combining for-in / while / break / continue
// ============================================
import Foundation
let logs = [
    "[INFO] 2026-07-15 08:00:00 Server started",
    "[ERROR] 2026-07-15 08:05:23 DB connection timeout",
    "[INFO] 2026-07-15 08:10:45 Cache warmed up",
    "[ERROR] 2026-07-15 08:15:30 Disk I/O error",
    "[WARN] 2026-07-15 08:20:00 Memory usage 85%",
    "[ERROR] 2026-07-15 08:25:10 Request failed: timeout",
    "[INFO] 2026-07-15 08:30:00 Health check OK",
    "[DEBUG] 2026-07-15 08:35:00 Query plan: index scan",
    "[ERROR] 2026-07-15 08:40:00 Connection pool exhausted"
]
var stats = (info: 0, warn: 0, error: 0, debug: 0)
var errorLines: [String] = []
for entry in logs {
    if entry.hasPrefix("[DEBUG]") {
        stats.debug += 1
        continue
    }
    if entry.hasPrefix("[ERROR]") {
        stats.error += 1
        errorLines.append(entry)
    } else if entry.hasPrefix("[WARN]") {
        stats.warn += 1
    } else if entry.hasPrefix("[INFO]") {
        stats.info += 1
    }
}
print("=== Log Analysis Report ===")
print("Total entries: \(logs.count)")
print("INFO: \(stats.info) | WARN: \(stats.warn) | ERROR: \(stats.error) | DEBUG: \(stats.debug)")
if stats.error > 0 {
    print("\n=== Error Details ===")
    var i = 0
    while i < errorLines.count {
        print("\(i + 1). \(errorLines[i])")
        i += 1
    }
    print("\nError rate: \(Double(stats.error) / Double(logs.count) * 100)%")
}