{"id":2728,"date":"2026-02-05T11:44:29","date_gmt":"2026-02-05T11:44:29","guid":{"rendered":"https:\/\/demo.materiamedica.net\/demo6\/?p=2728"},"modified":"2026-02-05T11:44:29","modified_gmt":"2026-02-05T11:44:29","slug":"chapter-71-functions","status":"publish","type":"post","link":"https:\/\/demo.materiamedica.net\/demo6\/chapter-71-functions\/","title":{"rendered":"Chapter 71: Functions"},"content":{"rendered":"1. What is a function? (the most honest explanation)<\/h3>\n
A function<\/strong> is a named piece of reusable code that:<\/p>\n\n- takes zero or more inputs<\/strong> (parameters)<\/li>\n
- does some work<\/li>\n
- optionally returns<\/strong> a result<\/li>\n<\/ul>\n
Think of a function as a small worker<\/strong> inside your program:<\/p>\n\n- You give it instructions<\/strong> (parameters)<\/li>\n
- It does its job<\/strong><\/li>\n
- It hands back a result<\/strong> (or nothing)<\/li>\n<\/ul>\n
Functions are the building blocks<\/strong> of every non-trivial program.<\/p>\n2. The basic syntax \u2014 all the common forms<\/h3>\nForm 1 \u2013 Simplest function (no parameters, no return)<\/h4>\n\n
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Swift<\/div>\n
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func sayHello() {\r\n print(\"Hello, Hyderabad! \ud83c\udf36\ufe0f\")\r\n}\r\n\r\n\/\/ Call it\r\nsayHello() \/\/ prints: Hello, Hyderabad! \ud83c\udf36\ufe0f<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nForm 2 \u2013 With parameters (most common)<\/h4>\n\n
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Swift<\/div>\n
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func greet(name: String) {\r\n print(\"Namaste, \\(name)! \ud83d\udc4b\")\r\n}\r\n\r\ngreet(name: \"Rahul\") \/\/ Namaste, Rahul! \ud83d\udc4b\r\ngreet(name: \"Priya\") \/\/ Namaste, Priya! \ud83d\udc4b<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nImportant<\/strong>: In Swift, when you call<\/strong> the function, you must label<\/strong> the arguments (unless you use _ \u2014 more later).<\/p>\nForm 3 \u2013 With return value<\/h4>\n\n
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func add(_ a: Int, _ b: Int) -> Int {\r\n return a + b\r\n}\r\n\r\nlet sum = add(7, 8) \/\/ 15\r\nprint(sum)<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nShorthand return<\/strong> (very common & clean):<\/p>\n\n
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Swift<\/div>\n
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func multiply(_ a: Int, _ b: Int) -> Int {\r\n a * b \/\/ implicit return \u2014 no `return` keyword needed\r\n}\r\n\r\nprint(multiply(6, 7)) \/\/ 42<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nForm 4 \u2013 Multiple parameters + labels<\/h4>\n\n
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func introduce(name: String, age: Int, city: String) {\r\n print(\"\\(name) is \\(age) years old and lives in \\(city).\")\r\n}\r\n\r\nintroduce(name: \"Sneha\", age: 24, city: \"Hyderabad\")<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nYou can make some labels external<\/strong> and some internal<\/strong>:<\/p>\n\n
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func greet(person name: String, from city: String) {\r\n print(\"Namaste \\(name)! Greetings from \\(city)!\")\r\n}\r\n\r\ngreet(person: \"Aarav\", from: \"Bengaluru\")<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n3. Real-life examples \u2014 functions you will actually write<\/h3>\nExample 1 \u2013 Format currency (very common)<\/h4>\n\n
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Swift<\/div>\n
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func formatIndianCurrency(_ amount: Double) -> String {\r\n let formatter = NumberFormatter()\r\n formatter.numberStyle = .currency\r\n formatter.currencyCode = \"INR\"\r\n formatter.currencySymbol = \"\u20b9\"\r\n formatter.maximumFractionDigits = 2\r\n \r\n return formatter.string(from: NSNumber(value: amount)) ?? \"\u20b90.00\"\r\n}\r\n\r\nlet price = 12499.99\r\nprint(\"Price: \\(formatIndianCurrency(price))\") \/\/ Price: \u20b912,499.99<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nExample 2 \u2013 Validate email (very common in forms)<\/h4>\n\n
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func isValidEmail(_ email: String) -> Bool {\r\n let emailRegex = \"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\\\.[A-Za-z]{2,64}\"\r\n let emailPredicate = NSPredicate(format: \"SELF MATCHES %@\", emailRegex)\r\n \r\n return emailPredicate.evaluate(with: email)\r\n}\r\n\r\nlet testEmails = [\r\n \"rahul@example.com\",\r\n \"priya@gmail.com\",\r\n \"invalid-email\",\r\n \"a@b.c\",\r\n \"test@company.co.in\"\r\n]\r\n\r\nfor email in testEmails {\r\n print(\"\\(email): \\(isValidEmail(email) ? \"valid\" : \"invalid\")\")\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nExample 3 \u2013 Calculate discount (business logic)<\/h4>\n\n
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func calculateFinalPrice(\r\n basePrice: Double,\r\n quantity: Int,\r\n discountPercent: Double = 0,\r\n taxRate: Double = 0.18\r\n) -> Double {\r\n let subtotal = basePrice * Double(quantity)\r\n let discountAmount = subtotal * (discountPercent \/ 100)\r\n let priceAfterDiscount = subtotal - discountAmount\r\n let taxAmount = priceAfterDiscount * taxRate\r\n \r\n return priceAfterDiscount + taxAmount\r\n}\r\n\r\nlet final = calculateFinalPrice(\r\n basePrice: 1499.99,\r\n quantity: 2,\r\n discountPercent: 10,\r\n taxRate: 0.18\r\n)\r\n\r\nprint(\"Final amount: \u20b9\\(String(format: \"%.2f\", final))\")<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nExample 4 \u2013 Filter active users (very common in social \/ admin apps)<\/h4>\n\n
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struct User {\r\n let id: Int\r\n let name: String\r\n let isActive: Bool\r\n let lastActive: Date?\r\n}\r\n\r\nfunc activeUsers(from users: [User], since daysAgo: Int = 30) -> [String] {\r\n let cutoff = Date().addingTimeInterval(-Double(daysAgo * 24 * 60 * 60))\r\n \r\n return users\r\n .filter { $0.isActive || ($0.lastActive ?? .distantPast) >= cutoff }\r\n .map { $0.name }\r\n}\r\n\r\nlet users = [\r\n User(id: 1, name: \"Rahul\", isActive: true, lastActive: nil),\r\n User(id: 2, name: \"Priya\", isActive: false, lastActive: Date().addingTimeInterval(-15*24*60*60)),\r\n User(id: 3, name: \"Aarav\", isActive: false, lastActive: Date().addingTimeInterval(-45*24*60*60))\r\n]\r\n\r\nlet activeNames = activeUsers(from: users)\r\nprint(\"Active users:\", activeNames)<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n5. Very Common Beginner Mistakes & Correct Habits<\/h3>\n\n
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\n\n\n| Mistake<\/th>\n | Wrong \/ Risky code<\/th>\n | Correct \/ Better habit<\/th>\n | Why?<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Forgetting to return value<\/td>\n | func add(a: Int, b: Int) -> Int { a + b }<\/td>\n | return a + b or use implicit return<\/td>\n | Compile error if missing<\/td>\n<\/tr>\n |
\n| Using var for parameters unnecessarily<\/td>\n | func greet(name: String) { name = “Hello” + name }<\/td>\n | Parameters are let by default \u2014 good!<\/td>\n | Prevents accidental mutation<\/td>\n<\/tr>\n |
\n| Force-unwrapping in functions<\/td>\n | func getName(user: User?) -> String { user!.name }<\/td>\n | guard let user else { return “Guest” }<\/td>\n | Safer, better error handling<\/td>\n<\/tr>\n |
\n| Too many parameters<\/td>\n | func createUser(name, age, city, email, phone, \u2026)<\/td>\n | Use struct \/ DTO instead<\/td>\n | More readable, easier to extend<\/td>\n<\/tr>\n |
\n| Side-effects in pure functions<\/td>\n | func calculateTotal(price: Double) -> Double { print(“Calculating\u2026”); return price * 1.18 }<\/td>\n | Keep functions pure when possible<\/td>\n | Easier to test, predict<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 6. Quick Reference \u2013 Function patterns you will use most<\/h3>\n\n \n \n\n\n| Goal<\/th>\n | Most idiomatic style<\/th>\n | Notes \/ Tip<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Simple action (no return)<\/td>\n | func log(message: String) { print(message) }<\/td>\n | Side-effect functions<\/td>\n<\/tr>\n | \n| Pure calculation<\/td>\n | func add(_ a: Int, _ b: Int) -> Int { a + b }<\/td>\n | Implicit return, no return keyword<\/td>\n<\/tr>\n | \n| Optional return<\/td>\n | func findUser(id: Int) -> User? { \u2026 }<\/td>\n | Return nil when not found<\/td>\n<\/tr>\n | \n| Multiple outputs<\/td>\n | func divide(_ a: Double, by b: Double) -> (quotient: Double, remainder: Double)<\/td>\n | Use tuple or custom struct<\/td>\n<\/tr>\n | \n| Default parameters<\/td>\n | func greet(name: String = “Guest”) { \u2026 }<\/td>\n | Very common for optional arguments<\/td>\n<\/tr>\n | \n| Throwing function<\/td>\n | func loadData() throws -> Data { \u2026 }<\/td>\n | Use try, do-catch when calling<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 7. Small Practice \u2013 Try these<\/h3>\n\n- Write a function greetUser(name: String, age: Int) that prints: “Namaste [name]! You are [age] years old.”<\/li>\n
- Write a function calculateDiscountedPrice(original: Double, discountPercent: Double = 10) -> Double<\/li>\n
- Write a function isStrongPassword(_ password: String) -> Bool that checks:\n
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