String templates and interpolation in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a string template in Kotlin?

A string template in Kotlin is a way to include variables or expressions inside a string by using the $ symbol before the variable name or ${} for expressions.

beginner

How do you include a variable name inside a string using Kotlin string templates?

You write the string like this: "Hello, $name!". Kotlin replaces $name with the value of the variable name.

beginner

How do you include an expression like 2 + 3 inside a Kotlin string template?

You use curly braces around the expression: "The sum is ${2 + 3}". Kotlin calculates the expression and inserts the result.

intermediate

What happens if you want to include a literal dollar sign $ in a Kotlin string template?

You escape it by using \$. For example, "Price is \$5" will show Price is $5.

intermediate

Can you use string templates with multiline strings in Kotlin?

Yes! You can use string templates inside triple-quoted strings """...""". Variables and expressions inside $ or ${} will be replaced as usual.

How do you insert the value of a variable age into a Kotlin string?

A "I am $age years old"

B "I am age years old"

C "I am ${age}"

D "I am ${age years old}"

Use $age or ${age} to insert the variable value. Option A is correct and simplest.

What is the output of: val x = 5; println("x + 2 = ${x + 2}")?

A x + 2 = 5 + 2

B x + 2 = x + 2

C x + 2 = ${x + 2}

D x + 2 = 7

The expression inside ${} is evaluated, so it prints 7.

How do you write a literal dollar sign in a Kotlin string template?

A $$

B \$

C $

D \\$

Use a backslash before the dollar sign to escape it: \$.

Which of these is a valid Kotlin string template expression?

A "Hello, ${user.name!}"

B "Hello, $user.name!"

C "Hello, ${user.name}!"

D "Hello, $user.name!" with quotes

You must use ${} for expressions like accessing a property.

Can you use string templates inside triple-quoted strings in Kotlin?

A Yes, variables and expressions are replaced.

B No, string templates don't work in triple quotes.

C Only variables work, not expressions.

D Only expressions work, not variables.

Triple-quoted strings support string templates fully.

Explain how to use string templates in Kotlin to include variables and expressions inside strings.

Think about how you write a sentence with a variable inside.

Describe how to include a literal dollar sign character in a Kotlin string that uses string templates.

Remember that $ is special in string templates.

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