Introduction to Swift

Reviewed & published by Brayan K

Swift is Apple's modern, fast, and safe programming language for building apps across iOS, macOS, watchOS, and tvOS, introduced in 2014 to replace Objective-C.

Part of the free Swift course at LearnCodingFast — hands-on lessons with worked examples and the output they print, plus practice exercises and a quick quiz.

By the end of this lesson you'll know what Swift is and where it runs, you'll understand print() and comments, and you'll have written and run your very first Swift program.

What You'll Learn in This Lesson

• • What Swift is — Apple's modern, fast, safe language for iOS and macOS
• • Where Swift runs: Xcode, Swift Playgrounds, and free online editors
• • How to show output with print()
• • How to leave notes in your code with single- and multi-line comments
• • How to drop values into text with string interpolation \(name)
• • How to write, read, and run a complete first Swift program

1️⃣ What is Swift (and where does it run)?

Swift is Apple's modern, fast, and safe programming language. Apple introduced it in 2014 to replace the older Objective-C, and it's now how almost every new iPhone, iPad, Mac, Apple Watch, and Apple TV app is built. "Safe" means the language is designed to catch whole classes of mistakes before your program runs, so your apps crash far less often.

So where do you actually write Swift? You have three common homes for it: Xcode (Apple's free, full code editor on the Mac, used to build real apps), Swift Playgrounds (a friendly app on Mac and iPad for learning and experimenting), and free online editors such as swiftfiddle.com or Replit that run in any browser. For this course, an online editor is the quickest way to start — you don't need a Mac yet.

2️⃣ Your first program: print() and comments

Every Swift journey starts with output. The print() function takes whatever you put between its parentheses and shows it in the console. Text goes inside "double quotes"; numbers don't need quotes. Anything after // is a comment — a note for humans that Swift ignores. Read this worked example, then run it and confirm the output matches.

// This is a comment — Swift ignores everything after the //.
// Comments are notes for humans; they never run.

/* You can also write a comment that
   spans several lines like this. */

// print(...) shows a line of text in the console (the output panel).
print("Hello, World!")          // shows: Hello, World!
print("I'm learning Swift!")    // shows: I'm learning Swift!

// You can print numbers too — no quotes needed for numbers.
print(2 + 2)                    // shows: 4

Now a slightly bigger first program. A let creates a constant — a named value. The real magic is string interpolation: write \(name) inside a string and Swift swaps in the value of name. It reads far better than sticking pieces of text together by hand.

// A first real program: greet a person by name.

// 'let' makes a constant — a named value that never changes.
let name = "Sam"
let year = 2014

// \(...) is "string interpolation": Swift drops the value into the text.
print("Hi \(name)! Welcome to Swift.")     // Hi Sam! Welcome to Swift.
print("Swift launched in \(year).")        // Swift launched in 2014.

// print can join values with commas — note the automatic spaces.
print("Two", "plus", "two", "is", 2 + 2)   // Two plus two is 4

3️⃣ Your turn: print and comment

Time to write some code. The program below is almost finished — just fill in the two blanks marked ___ using the // 👉 hints, then run it and check your output against the expected lines.

// 🎯 YOUR TURN — replace each ___ then run it (try SwiftFiddle, link below).

// 1) Print a friendly greeting of your choice
print(___)                 // 👉 put your text inside "double quotes"

// 2) Print the answer to 10 + 5  (numbers need no quotes)
print(___)                 // 👉 replace ___ with  10 + 5

// 3) Write a // comment above the next line saying what it does
print("Comments are free — use them!")

// ✅ Expected output (example):
//    Hello there!
//    15
//    Comments are free — use them!

4️⃣ Your turn: interpolate your own details

One more guided exercise, this time with string interpolation. Fill in the name and age blanks, then run it — the print line already works once your constants exist.

// 🎯 YOUR TURN — fill in the blanks to greet YOU.

// 1) Make a constant 'name' holding your name (text in "double quotes")
let name = ___             // 👉 e.g. "Alex"

// 2) Make a constant 'age' holding your age (a whole number, no quotes)
let age = ___              // 👉 e.g. 21

// This line already works once your constants exist.
// \(name) and \(age) get replaced by their values.
print("My name is \(name) and I am \(age).")

// ✅ Expected output (example):
//    My name is Alex and I am 21.

Common Errors (and the fix)

• "Cannot find Xcode" / nothing happens when you click run: Xcode only exists on a Mac and is a big download. If you're on Windows, Linux, or just starting out, skip it — use swiftfiddle.com in your browser instead.
• Nothing prints because you used return instead of print: return hands a value back inside a function but shows nothing on screen. To see output, use print(...).
• "Unterminated string literal": you forgot a quote, like print("Hello). Swift text needs a matching pair of "double quotes": print("Hello").
• "Cannot find 'name' in scope": you used a value before creating it. Declare it first with let name = "Sam", then use \(name).

Pro Tips

• 💡 Print often while learning: add a print(...) to check a value any time you're unsure what's happening.
• 💡 Comment the "why": good comments explain why a line exists, not just what it obviously does.
• 💡 No semicolons needed: Swift ends a statement at the end of the line, so leave the ; off.

📋 Quick Reference — Swift Basics

Mini-Challenge: About-Me Card

No blanks this time — just a brief and an outline to keep you on track. Write it yourself, run it on SwiftFiddle, and check your output against the example in the comments.

// 🎯 MINI-CHALLENGE: About-Me card
// 1. Make three constants with 'let':
//      name (your name), city (where you live), and favourite (a hobby).
// 2. Print three lines using string interpolation \(...) :
//      "Name: <name>", "City: <city>", "I love <favourite>."
// 3. BONUS: add a // comment above each print saying what it shows.
//
// ✅ Example output:
//    Name: Sam
//    City: Leeds
//    I love coding.

// your code here

🎉 Lesson Complete!

• ✅ Swift is Apple's modern, fast, safe language for iOS, macOS, and beyond
• ✅ It runs in Xcode, Swift Playgrounds, and free online editors (no Mac needed to start)
• ✅ print(...) shows output; // and /* */ add comments Swift ignores
• ✅ \(value) interpolation drops a value straight into a string

Practice quiz

Continue this course

• Next: Variables and Data Types — Strings, integers, doubles, booleans — and Swift's type inference system

Frequently asked questions

Do I need a Mac to learn Swift?

No. You can write and run Swift entirely in your browser using a free site like SwiftFiddle or Replit — no installation and no Apple device required. You only need macOS and Xcode later, when you want to build and ship actual iOS or macOS apps.

What is print() actually doing?

print() writes a line of text to the console — the output area where your program's results appear. It is the simplest way to see what your code is doing, and you will use it constantly while learning to check that values are what you expect.

What does \(name) mean inside a string?

That is string interpolation. Swift replaces \(name) with the current value of name. So if name is "Sam", then print("Hi \(name)") prints "Hi Sam". It is cleaner than gluing pieces of text together with the + sign.

Why does Swift not use semicolons at the end of lines?

Swift treats the end of a line as the end of a statement, so semicolons are optional. Leaving them off keeps code clean and readable. You only need a semicolon if you want to put two statements on the same line.