String templates and interpolation in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple string template

What is the output of this Kotlin code using string templates?

Kotlin

val name = "Anna"
val age = 25
println("My name is $name and I am $age years old.")

A My name is Anna and I am 25 years old.

B My name is $name and I am $age years old.

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

D My name is name and I am 25 years old.

💡 Hint

Remember that $variable inside a string replaces with the variable's value.

In Kotlin, $name and $age inside a string are replaced by their values, so the output shows the actual values.

❓ Predict Output

intermediate

Using expressions inside string templates

What will this Kotlin code print?

Kotlin

val x = 5
val y = 3
println("Sum of $x and $y is ${x + y}")

A Sum of 5 and 3 is 53

B Sum of x and y is x + y

C Sum of 5 and 3 is ${x + y}

D Sum of 5 and 3 is 8

💡 Hint

Expressions inside ${} are evaluated before printing.

The expression ${x + y} calculates 5 + 3 and inserts 8 into the string.

🔧 Debug

advanced

Identify the error in string interpolation

What error does this Kotlin code produce?

Kotlin

val count = 10
println("You have $count items in your cart")
println("Next item price is $price")

A Syntax error: missing curly braces

B No error, prints both lines correctly

C Unresolved reference: price

D Type mismatch error

💡 Hint

Check if all variables used inside strings are declared.

Variable 'price' is not declared anywhere, so Kotlin reports 'Unresolved reference: price'.

❓ Predict Output

advanced

Complex string interpolation with multiline string

What is the output of this Kotlin code?

Kotlin

val user = "Bob"
val score = 42
val message = """
Hello, $user!
Your score is ${score * 2}.
Good luck!
"""
println(message.trim())

A

Hello, $user!
Your score is ${score * 2}.
Good luck!

B

Hello, Bob!
Your score is 84.
Good luck!

C

Hello, Bob!
Your score is score * 2.
Good luck!

D Hello, Bob! Your score is 42. Good luck!

💡 Hint

Multiline strings keep line breaks and expressions inside ${} are evaluated.

The multiline string preserves line breaks and evaluates ${score * 2} as 84.

🧠 Conceptual

expert

Understanding string template evaluation order

Consider this Kotlin code snippet: val a = 3 val b = 4 println("Result: ${a + b}") println("Result: $a + $b") What will be the output?

A

Result: 7
Result: 3 + 4

B

Result: 7
Result: 7

C

Result: 7
Result: $a + $b

D

Result: a + b
Result: 3 + 4

💡 Hint

Expressions inside ${} are evaluated, but $variable just inserts the variable's value.

The first println evaluates ${a + b} to 7. The second prints the values of a and b separately with a plus sign in between.

Practice

1. What is the correct way to include a variable name inside a Kotlin string using string templates?

easy

A. println("Hello, +name+")

B. println("Hello, {name}!")

C. println("Hello, $name!")

D. println("Hello, %name%!")

Solution

1. Step 1: Understand Kotlin string templates

   Kotlin uses $variable to insert variable values inside strings.

2. Step 2: Identify correct syntax for variable insertion

   The syntax $name directly inserts the value of name into the string.

3. Final Answer:

   println("Hello, $name!") -> Option C

4. Quick Check:

   Use $variable for string templates [OK]

Hint: Use $variable to insert variables inside strings [OK]

Common Mistakes:

• Using curly braces without $ like {name}
• Concatenating with + inside strings
• Using % signs instead of $

2. Which of the following is the correct syntax to include an expression inside a Kotlin string template?

easy

A. println("Sum is ${a + b}")

B. println("Sum is $a + $b")

C. println("Sum is $[a + b]")

D. println("Sum is $(a + b)")

Solution

1. Step 1: Recall expression syntax in string templates

   Kotlin uses ${expression} to evaluate expressions inside strings.

2. Step 2: Identify correct expression usage

   ${a + b} correctly calculates the sum and inserts it.

3. Final Answer:

   println("Sum is ${a + b}") -> Option A

4. Quick Check:

   Use ${expression} for calculations inside strings [OK]

Hint: Use ${} to insert expressions inside strings [OK]

Common Mistakes:

• Using $a + $b prints variables separately, not sum
• Using square brackets [] instead of curly braces
• Using parentheses () without $

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

val price = 10
val tax = 2
println("Total: ${price + tax}")

medium

A. Total: 10 + 2

B. Total: 12

C. Total: ${price + tax}

D. Total: price + tax

Solution

1. Step 1: Evaluate the expression inside the string template

   The expression ${price + tax} adds 10 + 2 = 12.

2. Step 2: Print the resulting string

   The string becomes "Total: 12" and is printed.

3. Final Answer:

   Total: 12 -> Option B

4. Quick Check:

   Expression inside ${} is evaluated [OK]

Hint: Expressions inside ${} are calculated before printing [OK]

Common Mistakes:

• Printing the expression literally without evaluation
• Confusing $variable with ${expression}
• Expecting concatenation without braces

4. Identify the error in this Kotlin code snippet:

val count = 5
println("Count is $count+1")

medium

A. It will print 'Count is 5+1' literally, not sum

B. Runtime error because of invalid string

C. Syntax error due to missing braces

D. It will print 'Count is 6' correctly

Solution

1. Step 1: Understand how $count+1 is interpreted

   Kotlin treats $count as variable and +1 as plain text, so it prints "5+1" literally.

2. Step 2: Correct way to calculate sum in string

   Use ${count + 1} to evaluate the sum inside the string.

3. Final Answer:

   It will print 'Count is 5+1' literally, not sum -> Option A

4. Quick Check:

   Use ${} for expressions, else prints text [OK]

Hint: Use ${} to calculate expressions, else prints text [OK]

Common Mistakes:

• Assuming $count+1 calculates sum automatically
• Missing braces for expressions
• Confusing string concatenation with templates

5. You want to print the price with a dollar sign, for example: $20. Which Kotlin string correctly shows the dollar sign before the number stored in price?

hard

A. println("$price")

B. println("\$price")

C. println("$\$price")

D. println("\$$price")

Solution

1. Step 1: Understand escaping dollar sign in Kotlin strings

   To print a literal dollar sign, use \$ to escape it.

2. Step 2: Combine escaped dollar sign with variable

   "\$$price" prints a literal $ followed by the value of price.

3. Final Answer:

   println("\$$price") -> Option D

4. Quick Check:

   Escape $ with \$ to print it literally [OK]

Hint: Escape $ as \$ to print dollar sign literally [OK]

Common Mistakes:

• Not escaping $ prints variable name or causes error
• Using $\$ instead of \$$
• Confusing escape sequences