String interpolation in Swift

Introduction

String interpolation lets you easily put values like numbers or text inside a string. It helps make messages that change based on data.

Showing a user's name inside a welcome message.

Displaying the result of a calculation in a sentence.

Creating a sentence that includes the current date or time.

Building a message that includes values from variables.

Syntax

Swift

let message = "Hello, \(name)!"

Use \( ) inside a string to insert a value or expression.

You can put variables, math, or function calls inside the parentheses.

Examples

Insert a number variable inside a string.

Swift

let age = 25
let greeting = "I am \(age) years old."

Insert a text variable inside a string.

Swift

let name = "Anna"
let welcome = "Welcome, \(name)!"

Insert a math expression inside a string.

Swift

let a = 5
let b = 3
let sum = "Sum is \(a + b)"

Sample Program

This program creates a message that includes a name and number using string interpolation, then prints it.

Swift

let userName = "Sam"
let items = 3
let message = "Hello, \(userName)! You have \(items) new messages."
print(message)

Important Notes

String interpolation works only inside double quotes " ".

You can put any Swift expression inside \( ), not just variables.

It helps avoid long string concatenations with + signs.

Summary

String interpolation inserts values inside strings easily.

Use \( ) inside double quotes to add variables or expressions.

It makes building dynamic messages simple and readable.

Practice

1. What does string interpolation in Swift allow you to do?

easy

A. Convert a string to uppercase or lowercase

B. Create a new string by repeating characters multiple times

C. Split a string into an array of characters

D. Insert variables or expressions directly inside a string using \( )

Solution

1. Step 1: Understand string interpolation purpose

   String interpolation lets you put variables or expressions inside a string easily.

2. Step 2: Recognize the syntax

   Using \( ) inside double quotes inserts the value dynamically.

3. Final Answer:

   Insert variables or expressions directly inside a string using \( ) -> Option D

4. Quick Check:

   String interpolation = Insert variables with \( ) [OK]

Hint: Remember: \( ) inside quotes inserts values fast [OK]

Common Mistakes:

• Confusing interpolation with string repetition
• Trying to use single quotes instead of double quotes
• Forgetting the backslash before parentheses

2. Which of the following is the correct way to use string interpolation in Swift to show the value of variable score inside a string?

easy

A. "Your score is: ${score}"

B. "Your score is: score"

C. "Your score is: \(score)"

D. "Your score is: {score}"

Solution

1. Step 1: Identify correct interpolation syntax

   Swift uses \(variable) inside double quotes for interpolation.

2. Step 2: Check each option

   "Your score is: \(score)" uses \(score), which is correct. Others use wrong syntax.

3. Final Answer:

   "Your score is: \(score)" -> Option C

4. Quick Check:

   Swift interpolation = \(variable) [OK]

Hint: Use backslash and parentheses for variables inside strings [OK]

Common Mistakes:

• Using ${} like in other languages
• Forgetting the backslash before parentheses
• Not using double quotes around the string

3. What will be the output of the following Swift code?

let name = "Anna"
let age = 30
print("\(name) is \(age) years old.")

medium

A. Anna is 30 years old.

B. name is age years old.

C. \(name) is \(age) years old.

D. Anna is \(age) years old.

Solution

1. Step 1: Understand variable values

   name = "Anna", age = 30.

2. Step 2: Apply string interpolation

   "\(name)" becomes "Anna", "\(age)" becomes "30" in the string.

3. Final Answer:

   Anna is 30 years old. -> Option A

4. Quick Check:

   Interpolation replaces variables with values [OK]

Hint: Replace \(variable) with its value inside the string [OK]

Common Mistakes:

• Printing the literal \(name) instead of value
• Confusing variable names with strings
• Missing backslash causing no interpolation

4. Identify the error in this Swift code snippet using string interpolation:

let temperature = 22
print("The temperature is (temperature) degrees.")

medium

A. Missing backslash before parentheses in interpolation

B. Variable temperature is not declared

C. Using single quotes instead of double quotes

D. Parentheses should be square brackets

Solution

1. Step 1: Check interpolation syntax

   Interpolation requires a backslash before parentheses: \(variable).

2. Step 2: Identify missing backslash

   Code uses (temperature) without backslash, so it won't interpolate.

3. Final Answer:

   Missing backslash before parentheses in interpolation -> Option A

4. Quick Check:

   Backslash is required for interpolation [OK]

Hint: Always add \ before (variable) in strings [OK]

Common Mistakes:

• Forgetting the backslash
• Using wrong quote types
• Assuming parentheses alone interpolate

5. You want to create a message that shows the total price including tax. Given price = 50 and taxRate = 0.1, which Swift code correctly uses string interpolation to print "Total price: 55.0"?

hard

A. print("Total price: \(price + taxRate)")

B. print("Total price: \(price * (1 + taxRate))")

C. print("Total price: \(price * taxRate)")

D. print("Total price: \(price + taxRate * 100)")

Solution

1. Step 1: Calculate total price with tax

   Total price = price * (1 + taxRate) = 50 * 1.1 = 55.0.

2. Step 2: Check each option's expression

   print("Total price: \(price * (1 + taxRate))"): print("Total price: \(price * (1 + taxRate))") = 55.0 correct. A: \(price + taxRate) = 50.1 wrong. C: \(price * taxRate) = 5.0 (tax only) wrong. D: \(price + taxRate * 100) = 60 wrong.

3. Final Answer:

   print("Total price: \(price * (1 + taxRate))") -> Option B

4. Quick Check:

   Use price * (1 + taxRate) for total [OK]

Hint: Multiply price by (1 + taxRate) inside \( ) [OK]

Common Mistakes:

• Adding taxRate directly instead of multiplying
• Forgetting parentheses around (1 + taxRate)
• Multiplying taxRate by 100 incorrectly