Swift: المتغيرات والثوابت في Swift

var orderCount = "8500"
// Next month, orders grew by 1200
orderCount = orderCount + 1200  // Compilation error!

// Correct data type definitions
var orderCount = 8500          // Int
var productName = "Headphones" // String
var unitPrice = 49.99          // Double
orderCount = orderCount + 1200
let totalRevenue = Double(orderCount) * unitPrice
print("Product: \(productName)")
print("Monthly sales: \(orderCount), Revenue: $\(totalRevenue)")

// Variable values can be modified at any time
var score = 0
score = 85           // Update value
score = score + 10   // Recalculate based on current value

// Constants cannot be modified after assignment
let maxLoginAttempts = 5
// maxLoginAttempts = 6  // ❌ Compilation error
let pi = 3.14159
let appName = "MyApp"

// ============================================
// Use variables for cart quantity, constants for product info
// ============================================
// Constants: Fixed information
let productName = "Wireless Headphones"
let unitPrice = 79.99
// Variable: Changing data
var quantity = 1
print("Product: \(productName)")
print("Unit price: $\(unitPrice)")
print("Current quantity: \(quantity)")
// User increased the purchase quantity
quantity = 3
let total = unitPrice * Double(quantity)
print("Buying \(quantity) items, Total: $\(total)")

let year = 2026
var count = -100
let population: Int = 8_000_000_000  // Underscores improve readability

let temperature = 36.5
var price = 19.99
let taxRate = 0.08

let userName = "Alice"
var message = "Welcome to Swift"
let empty = ""  // Empty string

let isLoggedIn = false
var isAvailable = true
let isGreater = 10 > 5  // Comparison automatically produces true

// ============================================
// Storing user information with different types
// ============================================
let userName = "Bob"        // String
var age = 28                // Int
let height = 1.85           // Double
var isPremiumMember = false // Bool
print("Name: \(userName)")
print("Age: \(age)")
print("Height: \(height) m")
print("Member: \(isPremiumMember)")
// Type safety — the following line will not compile
// age = "twenty-eight"  // ❌ Cannot assign String to Int

let name: String = "Charlie"
var age: Int = 25
var price: Double = 29.99
let isActive: Bool = true

let apples = 3
let pricePerApple = 0.99
// let total = apples * pricePerApple     // ❌ Int and Double cannot multiply directly
let total = Double(apples) * pricePerApple  // ✅ Convert Int to Double

// ============================================
// Calculate order total, demonstrating type conversion
// ============================================
import Foundation
let itemCount = 5            // Int
let unitPrice = 12.99        // Double
let taxPercent = 0.08        // Double
// Int must be converted to Double for arithmetic
let subtotal = Double(itemCount) * unitPrice
let taxAmount = subtotal * taxPercent
let total = subtotal + taxAmount
print("Item count: \(itemCount)")
print("Unit price: $\(unitPrice)")
print("Subtotal: $\(subtotal)")
print("Tax (8%): $\(taxAmount)")
print("Total: $\(total)")
// Convert Double to String for text concatenation
let receipt = "Total: $" + String(format: "%.2f", total)
print(receipt)

// ============================================
// E-commerce order statistics summary
// Demonstrates variables, constants, data types, type conversion
// ============================================
import Foundation
// 1. Constants: Store info and fixed configuration
let storeName = "Swift Gear Shop"
let taxRate = 0.07
// 2. Variables: Mutable order data
var orderCount = 0
var totalRevenue = 0.0
// 3. Process first batch of orders
let price1 = 49.99
let qty1 = 3
orderCount += qty1
let subtotal1 = Double(qty1) * price1
totalRevenue += subtotal1
// 4. Process second batch of orders
let price2 = 129.00
let qty2 = 1
orderCount += qty2
let subtotal2 = Double(qty2) * price2
totalRevenue += subtotal2
// 5. Output statistics report
print("Store: \(storeName)")
print("=== Sales Statistics ===")
print("Items sold: \(orderCount)")
print("Total revenue: $\(totalRevenue)")
print("Estimated tax: $\(totalRevenue * taxRate)")
print("Net revenue: $\(totalRevenue * (1 - taxRate))")
let summary = "Processed " + String(orderCount) + " items today"
print(summary)