String interpolation in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple string interpolation

What is the output of this Swift code?

Swift

let name = "Alice"
let age = 30
print("My name is \(name) and I am \(age) years old.")

A My name is Alice and I am 30 years old.

B My name is \(name) and I am \(age) years old.

C My name is name and I am age years old.

D My name is Alice and I am age years old.

💡 Hint

Look at how variables are inserted inside the string using \(variable).

Swift replaces \(variable) with the value of the variable inside the string.

❓ Predict Output

intermediate

String interpolation with expressions

What will this Swift code print?

Swift

let x = 5
let y = 3
print("Sum: \(x + y), Product: \(x * y)")

A Sum: x + y, Product: x * y

B Sum: 8, Product: x * y

C Sum: 53, Product: 15

D Sum: 8, Product: 15

💡 Hint

Inside \( ), Swift evaluates the expression before inserting it.

The expressions x + y and x * y are calculated and their results inserted.

🔧 Debug

advanced

Identify the error in string interpolation

What error does this Swift code produce?

Swift

let celsius = 22
print("Current temperature is \celsius degrees.")

A Prints: Current temperature is temperature degrees.

B Prints: Current temperature is \temperature degrees.

C SyntaxError: Missing parentheses around variable in string interpolation

D RuntimeError: Variable temperature not found

💡 Hint

Check how variables are inserted inside strings in Swift.

Swift requires variables inside string interpolation to be inside parentheses: \(variable).

❓ Predict Output

advanced

String interpolation with multiline strings

What is the output of this Swift code?

Swift

let name = "Bob"
let score = 95
let message = """Hello, \(name)!\nYour score is \(score).\n"""
print(message)

A

Hello, Bob!
Your score is 95.

B

Hello, \(name)!
Your score is \(score).

C Hello, Bob! Your score is 95.

D

Hello, name!
Your score is score.

💡 Hint

Multiline strings keep line breaks and support interpolation the same way.

The multiline string inserts variable values and preserves line breaks.

🧠 Conceptual

expert

Effect of using backslash without parentheses in interpolation

What happens if you write this Swift code? let count = 10 print("Count is \count")

A Prints: Count is \count

B Compiler error due to missing parentheses in string interpolation

C Prints: Count is count

D Prints: Count is 10

💡 Hint

Swift requires parentheses around variables in string interpolation.

Without parentheses, the backslash is not recognized as interpolation and causes a syntax error.

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