Kotlin REPL and script mode - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, Kotlin!" in Kotlin REPL.

Kotlin

println([1])

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

AHello Kotlin

B"Hello, Kotlin!"

C'Hello, Kotlin!'

DHello, Kotlin!

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes around the string

Using single quotes which are for characters, not strings

In Kotlin, strings must be enclosed in double quotes. So to print a string, use println("string").

2fill in blank

medium

Complete the Kotlin script to declare a variable with value 10.

Kotlin

val number: Int = [1]

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

Aten

B"10"

C10

D10.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes which makes the value a string

Using a decimal number for an Int type

To assign an integer value to a variable, use the number without quotes. Quotes make it a string.

3fill in blank

hard

Fix the error in the Kotlin script to print the sum of two numbers.

Kotlin

val sum = 5 [1] 3
println(sum)

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition

Using division which changes the result

The plus sign (+) adds two numbers in Kotlin.

4fill in blank

hard

Fill both blanks to create a Kotlin map of words to their lengths.

Kotlin

val lengths = mapOf([1] to [2])

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

A"apple"

B5

C"banana"

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers as keys without quotes

Mixing up keys and values

Use a string as the key and its length as the value in the map.

5fill in blank

hard

Fill all three blanks to create a Kotlin script that filters a list for numbers greater than 3.

Kotlin

val filtered = listOf(1, 2, 3, 4, 5).filter { it [1] [2] }
println(filtered[3])

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

A>

B3

C.joinToString()

D.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than instead of greater than

Printing the list without formatting

The filter uses > 3 to select numbers greater than 3. The result is printed as a joined string.

Practice

1. What is the main purpose of Kotlin REPL?

easy

A. To run Kotlin code interactively line by line

B. To compile Kotlin code into Java bytecode

C. To create Android applications

D. To manage Kotlin project dependencies

Solution

1. Step 1: Understand REPL meaning

   Kotlin REPL stands for Read-Eval-Print Loop, which runs code interactively.

2. Step 2: Identify REPL use

   It lets you type and run Kotlin code line by line without compiling a full program.

3. Final Answer:

   To run Kotlin code interactively line by line -> Option A

4. Quick Check:

   Kotlin REPL = Interactive code running [OK]

Hint: REPL runs code line by line interactively [OK]

Common Mistakes:

• Confusing REPL with full project compilation
• Thinking REPL is for app deployment
• Assuming REPL manages dependencies

2. Which file extension is used for Kotlin script files?

easy

A. .kts

B. .skr

C. .kotlin

D. .kt

Solution

1. Step 1: Recall Kotlin file types

   Kotlin source files usually use .kt extension for normal programs.

2. Step 2: Identify script file extension

   Kotlin scripts use .kts extension to run code without full compilation.

3. Final Answer:

   .kts -> Option A

4. Quick Check:

   Kotlin script files = .kts [OK]

Hint: Scripts use .kts extension, not .kt [OK]

Common Mistakes:

• Choosing .kt which is for normal Kotlin files
• Assuming .kotlin or .skr are valid extensions
• Mixing script files with compiled files

3. What is the output of this Kotlin REPL session?

val x = 5
val y = 10
x + y

medium

A. 510

B. Error: undefined variables

C. x + y

D. 15

Solution

1. Step 1: Evaluate variable assignments

   x is assigned 5, y is assigned 10 in REPL environment.

2. Step 2: Calculate expression result

   x + y equals 5 + 10 which is 15.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add values assigned to variables for output [OK]

Common Mistakes:

• Concatenating numbers as strings (510)
• Printing expression text instead of result
• Assuming variables are undefined in REPL

4. Identify the error in this Kotlin script file example.kts:

val name = "Alice"
println(Name)

medium

A. Script files cannot use println

B. Variable 'Name' is not defined (case sensitive)

C. Missing semicolon after println statement

D. String literals must use single quotes

Solution

1. Step 1: Check variable usage

   Variable declared as 'name' but used as 'Name' which differs in case.

2. Step 2: Understand Kotlin case sensitivity

   Kotlin variables are case sensitive, so 'Name' is undefined causing error.

3. Final Answer:

   Variable 'Name' is not defined (case sensitive) -> Option B

4. Quick Check:

   Variable names are case sensitive [OK]

Hint: Check variable name case carefully [OK]

Common Mistakes:

• Thinking semicolons are mandatory
• Believing println is disallowed in scripts
• Using single quotes for strings in Kotlin

5. You want to quickly test a Kotlin function without creating a full project. Which approach is best?

hard

A. Write the function in Java and call it from Kotlin

B. Create a full Kotlin project and add the function

C. Use Kotlin REPL to define and test the function interactively

D. Write the function in a .kts script file and run it

Solution

1. Step 1: Compare quick testing methods

   Creating a full project is slow; writing Java adds complexity.

2. Step 2: Choose between script and REPL

   REPL lets you define and test functions interactively without saving files.

3. Step 3: Understand REPL advantage

   REPL is fastest for quick tests; scripts require saving and running files.

4. Final Answer:

   Use Kotlin REPL to define and test the function interactively -> Option C

5. Quick Check:

   REPL = fastest interactive testing [OK]

Hint: Use REPL for fastest interactive function testing [OK]

Common Mistakes:

• Assuming scripts are faster than REPL
• Thinking full projects are needed for tests
• Confusing Java code with Kotlin quick tests