String interpolation in Swift - Mini Project: Build & Apply

String interpolation

📖 Scenario: You are creating a simple program to greet users by their name and age. This is like writing a friendly note that includes their details.

🎯 Goal: Build a Swift program that uses string interpolation to combine variables into a greeting message.

📋 What You'll Learn

Create variables with exact names and values

Use string interpolation to build a greeting message

Print the final greeting message

💡 Why This Matters

🌍 Real World

String interpolation is used in apps to create messages, labels, and notifications that include user data or dynamic information.

💼 Career

Knowing string interpolation helps you build user-friendly interfaces and display information clearly in software development jobs.

1

Create user data variables

Create a variable called name and set it to the string "Alice". Create another variable called age and set it to the integer 30.

Swift

# Your code here

Hint

Use var to create variables and assign the exact values given.

2

Create a greeting message variable

Create a variable called greeting and set it to a string that uses string interpolation to include the name and age variables in this exact format: "Hello, my name is Alice and I am 30 years old."

Swift

var name = "Alice"
var age = 30
# Your code here

Hint

Use \(variableName) inside the string to insert variable values.

3

Modify the age variable

Change the value of the age variable to 31.

Swift

var name = "Alice"
var age = 30
var greeting = "Hello, my name is \(name) and I am \(age) years old."
age = 31
# Your code here

Hint

Assign the new value directly to the age variable.

4

Print the greeting message

Write a print statement to display the greeting variable.

Swift

var name = "Alice"
var age = 31
var greeting = "Hello, my name is \(name) and I am \(age) years old."
# Your code here

Hint

Use print(greeting) to show the message on the screen.

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