String concatenation vs templates in Kotlin - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to concatenate two strings using the + operator.

Kotlin

val greeting = "Hello, " [1] "World!"

Drag options to blanks, or click blank then click option'

A+

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using arithmetic operators like - or * instead of + for strings.

In Kotlin, the + operator is used to join (concatenate) strings.

2fill in blank

medium

Complete the code to use a string template to insert the variable name into the greeting.

Kotlin

val name = "Alice"
val greeting = "Hello, [1]!"

Drag options to blanks, or click blank then click option'

A{name}

Bname

C"name"

D$name

Attempts:

3 left

💡 Hint

Common Mistakes

Writing the variable name without $ inside the string.

Using curly braces without $.

In Kotlin, string templates use the $ symbol before a variable name to insert its value inside a string.

3fill in blank

hard

Fix the error in the string template to correctly include the variable age.

Kotlin

val age = 30
val message = "I am [1] years old."

Drag options to blanks, or click blank then click option'

A${age}

Bage

C$age

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using $variable without braces when followed by text.

Writing variable name without $.

When inserting expressions or variables in Kotlin strings, use ${variable} to clearly mark the variable inside the string.

4fill in blank

hard

Fill both blanks to create a map of words to their lengths, using string templates and a condition.

Kotlin

val words = listOf("apple", "bat", "carrot")
val lengths = {word: [1] for word in words if word.length [2] 3}

Drag options to blanks, or click blank then click option'

Aword.length

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of word.length for the value.

Using wrong comparison operators like < or ==.

The map uses word.length to get the length of each word. The condition filters words longer than 3 characters using >.

5fill in blank

hard

Fill all three blanks to create a message using string templates with expressions.

Kotlin

val x = 5
val y = 10
val message = "Sum of [1] and [2] is [3]"

Drag options to blanks, or click blank then click option'

Ax

By

C${x + y}

D$x

Attempts:

3 left

💡 Hint

Common Mistakes

Not using $ before variables inside strings.

Not using ${} for expressions.

Use $x and $y to insert variables, and ${x + y} to insert the sum expression inside the string.

Practice

1. What is the main difference between string concatenation and string templates in Kotlin?

easy

A. Templates require explicit conversion of variables to strings.

B. Concatenation uses + to join strings; templates insert variables with $ inside strings.

C. Concatenation is faster than templates in all cases.

D. Concatenation can only join strings, templates can join numbers only.

Solution

1. Step 1: Understand string concatenation

   Concatenation joins strings using the + operator and requires converting non-string variables to strings explicitly.

2. Step 2: Understand string templates

   Templates allow inserting variables directly inside strings using the $ symbol, making code cleaner and easier.

3. Final Answer:

   Concatenation uses + to join strings; templates insert variables with $ inside strings. -> Option B

4. Quick Check:

   Concatenation vs templates = C [OK]

Hint: Templates use $ for variables; concatenation uses + [OK]

Common Mistakes:

• Thinking templates need explicit conversion
• Believing concatenation is always faster
• Confusing syntax of templates and concatenation

2. Which of the following is the correct Kotlin syntax to insert a variable name into a string using templates?

easy

A. "Hello, {name}!"

B. "Hello, \$name!"

C. "Hello, ${name}!"

D. "Hello, " + name + "!"

Solution

1. Step 1: Recall string template syntax

   In Kotlin, to insert a variable inside a string, use $variable or ${variable} if expression is needed.

2. Step 2: Identify correct usage for variable insertion

   For simple variables, $name works, but to be safe and clear, especially in complex expressions, ${name} is preferred.

3. Final Answer:

   "Hello, ${name}!" -> Option C

4. Quick Check:

   Variable insertion = ${name} [OK]

Hint: Use ${variable} for safe template insertion [OK]

Common Mistakes:

• Using curly braces without $
• Using + inside templates
• Forgetting $ before variable

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

val age = 25
println("Age: " + age + " years")
println("Age: $age years")

medium

A. Age: 25 years
Age: 25 years

B. Age: 25 years
Age: $age years

C. Age: age years
Age: 25 years

D. Age: 25 years
Age: age years

Solution

1. Step 1: Evaluate first println with concatenation

   "Age: " + age + " years" converts age (25) to string and concatenates, resulting in "Age: 25 years".

2. Step 2: Evaluate second println with template

   "Age: $age years" inserts the value of age (25) directly, producing "Age: 25 years".

3. Final Answer:

   Age: 25 years Age: 25 years -> Option A

4. Quick Check:

   Concatenation and template output same = A [OK]

Hint: Templates insert values directly; concatenation converts explicitly [OK]

Common Mistakes:

• Expecting $age to print literally in templates
• Confusing variable name with value
• Missing conversion in concatenation

4. Identify the error in this Kotlin code snippet:

val score = 90
println("Your score is: $score") + " points"

medium

A. The + operator is used incorrectly outside println.

B. Variable score should be inside curly braces ${score}.

C. Missing semicolon after println statement.

D. String templates cannot be combined with + operator.

Solution

1. Step 1: Analyze the println statement

   println("Your score is: $score") prints the string with the variable inserted correctly.

2. Step 2: Check the use of + operator

   The + " points" is outside the println call, so it tries to add a string to the Unit result of println, causing an error.

3. Final Answer:

   The + operator is used incorrectly outside println. -> Option A

4. Quick Check:

   Operator placement error = B [OK]

Hint: Ensure + is inside println or use separate print [OK]

Common Mistakes:

• Thinking templates need curly braces always
• Adding + after println call
• Expecting semicolon in Kotlin

5. You want to create a message showing a user's name and age using Kotlin string templates. The variables are val name = "Anna" and val age = 30. Which code snippet correctly produces the output Hello, Anna! You are 30 years old.?

hard

A. println("Hello, " + name + "! You are " + age + " years old.")

B. println("Hello, $name! You are $age years old.")

C. println("Hello, ${name}! You are ${age} years old.")

D. Both B and C

Solution

1. Step 1: Check concatenation approach

   println("Hello, " + name + "! You are " + age + " years old.") uses concatenation with + operators and works but is less clean.

2. Step 2: Check template approaches

   String templates using $variable and ${variable} syntax are both correct: simple $variable vs ${variable}, both valid and produce the same output.

3. Step 3: Determine correct options

   Since both string template syntaxes produce the correct output, the option indicating both are correct is the answer.

4. Final Answer:

   Both B and C -> Option D

5. Quick Check:

   Templates with $ or ${} = D [OK]

Hint: Use $var or ${var} for templates; both work [OK]

Common Mistakes:

• Thinking only one template syntax is correct
• Confusing concatenation with templates
• Missing quotes around strings