Strings & String Interpolation

Text is everywhere in real apps. By the end of this lesson you'll create strings, splice values into them with interpolation \\(...) , write multiline literals with """ , and reach for the most common String methods with confidence.

Learn Strings & String Interpolation in our free Swift course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Swift course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

• • Create and join strings with + and +=
• • Splice values into text with interpolation \\(value)
• • Write multiline literals with triple quotes """
• • Use common methods: count , isEmpty , uppercased() , contains
• • Loop over a string's Character values

1️⃣ Creating & Joining Strings

A String is text in double quotes. Join strings with + , grow a var with += , and inspect length with count or emptiness with isEmpty .

2️⃣ String Interpolation

Interpolation drops a value straight into text with \\(...) — a backslash, then your expression in parentheses. You can run a real calculation inside the parentheses, not just name a variable.

3️⃣ Multiline Strings

Wrap text in triple quotes """ (on their own lines) to span multiple lines without escapes. Interpolation works inside them too — perfect for templates and messages.

4️⃣ Common Methods & Characters

Swift's String API is rich. Methods like uppercased() , contains , and hasPrefix return new values without changing the original. Looping over a string yields each Character — Swift's single-character type.

Your turn. Fill in the blanks, then run it and check the output.

Pro Tips

• 💡 Prefer interpolation over + for readability — especially when mixing numbers and text.
• 💡 String methods don't mutate. uppercased() returns a new string; the original is untouched.
• 💡 Trim whitespace with trimmingCharacters(in: .whitespaces) before validating user input.
• 💡 Need positional access? Convert with Array(myString) to index by integer when necessary.

Common Errors (and the fix)

• Single quotes don't work — 'a' is invalid. Swift text always uses "double quotes" .
• "Cannot subscript a value of type 'String' with an index of type 'Int'" — strings aren't integer-indexed. Use first / last or convert to an Array .
• Forgetting the backslash — "Hi (name)" prints literally. Interpolation needs \\(name) .
• "Binary operator '+' cannot be applied to 'String' and 'Int'" — convert the number first: "Age: " + String(age) , or just use interpolation.

📋 Quick Reference

Task

Code

Result

Interpolate

"Hi \\(name)"

Hi Sam

Length

s.count

number of chars

Empty?

s.isEmpty

true / false

Uppercase

s.uppercased()

new string

Contains

s.contains("x")

Multiline

"""...lines..."""

spans lines

Frequently Asked Questions

Mini-Challenge: Greeting Card

Build it, run it, and check your output against the example in the comments.

🎉 Lesson Complete!

• ✅ Strings use "double quotes" ; join with + / +=
• ✅ Interpolation with \\(value) beats concatenation for readability
• ✅ Multiline literals use triple quotes """
• ✅ Methods like count , isEmpty , uppercased() , contains return new values
• ✅ Next lesson: Arrays

Practice quiz

Continue this course

• Previous: Optionals & nil Safety
• Next: Arrays