Explicit type declaration in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with an explicit type.

Kotlin

val name: [1] = "Alice"

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

ABoolean

BInt

CString

DDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int or Boolean for text values.

Forgetting to specify the type explicitly.

The variable name is declared as a String type explicitly.

2fill in blank

medium

Complete the code to declare a variable with explicit integer type.

Kotlin

var age: [1] = 30

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

AInt

BDouble

CString

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using Double or String for whole numbers.

Not matching the type with the assigned value.

The variable age is declared as an Int type explicitly because it holds a whole number.

3fill in blank

hard

Fix the error in the explicit type declaration.

Kotlin

val isActive: [1] = true

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

AString

BBoolean

CInt

DDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using String type for Boolean values.

Assigning Boolean values as text strings.

The variable isActive should be declared as Boolean type and assigned a Boolean value true without quotes.

4fill in blank

hard

Fill both blanks to declare a variable with explicit Double type and assign a decimal value.

Kotlin

var price: [1] = [2]

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

ADouble

B30

C19.99

DInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int type for decimal numbers.

Assigning whole numbers instead of decimals.

The variable price is declared as Double type to hold decimal numbers, and assigned the decimal value 19.99.

5fill in blank

hard

Fill all three blanks to declare a variable with explicit type and assign a value correctly.

Kotlin

val [1]: [2] = [3]

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

AisAvailable

BBoolean

Cfalse

Dprice

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names.

Assigning Boolean values as strings.

Mismatch between type and assigned value.

The variable isAvailable is declared as Boolean type and assigned the Boolean value false.

Practice

1. What does explicit type declaration in Kotlin do?

easy

A. It automatically converts types without programmer input.

B. It tells Kotlin exactly what type a variable or value has.

C. It removes the need to use val or var.

D. It makes variables changeable by default.

Solution

1. Step 1: Understand explicit type declaration

   Explicit type declaration means telling Kotlin the exact type of a variable, like Int or String.

2. Step 2: Compare with other options

   The other options describe behaviors that are not related to explicit type declaration.

3. Final Answer:

   It tells Kotlin exactly what type a variable or value has. -> Option B

4. Quick Check:

   Explicit type declaration = telling exact type [OK]

Hint: Explicit means you say the type clearly [OK]

Common Mistakes:

• Thinking Kotlin guesses types without declaration
• Confusing explicit type with variable mutability
• Believing explicit type removes need for val/var

2. Which of the following is the correct syntax for explicit type declaration of a variable in Kotlin?

easy

A. var age: Int = 25

B. val height = Int 170

C. val name String = "Alice"

D. var weight = 70: Int

Solution

1. Step 1: Recall Kotlin variable declaration syntax

   Kotlin uses val or var followed by variable name, colon, type, then assignment.

2. Step 2: Check each option

   var age: Int = 25 matches this syntax: var age: Int = 25. Others have syntax errors.

3. Final Answer:

   var age: Int = 25 -> Option A

4. Quick Check:

   Correct syntax uses colon before type [OK]

Hint: Use colon (:) before type in declaration [OK]

Common Mistakes:

• Omitting colon before type
• Placing type after value
• Using wrong order of keywords

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

val number: Int = 10
var text: String = "Hello"
text = "Hi"
println(number)
println(text)

medium

A. Error: Cannot reassign val

B. 10\nHello

C. 10\nHi

D. 10\nnull

Solution

1. Step 1: Analyze variable declarations and assignments

   number is a val (fixed) with value 10. text is a var (changeable) initially "Hello", then changed to "Hi".

2. Step 2: Determine printed output

   Printing number outputs 10. Printing text outputs the updated value "Hi".

3. Final Answer:

   10 Hi -> Option C

4. Quick Check:

   val fixed, var changeable = 10 and Hi [OK]

Hint: val is fixed, var can change value [OK]

Common Mistakes:

• Thinking val can be reassigned
• Confusing initial and updated values
• Expecting syntax error for reassignment of var

4. Identify the error in this Kotlin code snippet:

val count: Int = 5
count = 10

medium

A. Missing type declaration for count

B. Variable count should be declared with var

C. Incorrect type Int assigned to count

D. Cannot reassign a value to val variable

Solution

1. Step 1: Understand val and var difference

   val means the variable is read-only and cannot be reassigned after initialization.

2. Step 2: Check the reassignment

   The code tries to assign 10 to count which is declared as val, causing an error.

3. Final Answer:

   Cannot reassign a value to val variable -> Option D

4. Quick Check:

   val is fixed, reassignment causes error [OK]

Hint: val variables cannot be reassigned [OK]

Common Mistakes:

• Thinking val variables can be changed
• Confusing val and var keywords
• Ignoring reassignment rules

5. You want to declare a variable score that can change and must hold decimal numbers. Which explicit type declaration is correct in Kotlin?

hard

A. var score: Double = 95.5

B. var score: Int = 95.5

C. val score: Double = 95.5

D. val score: Float = "95.5"

Solution

1. Step 1: Identify mutability requirement

   The variable score must be changeable, so use var, not val.

2. Step 2: Choose correct type for decimal numbers

   Decimal numbers require Double or Float, but value 95.5 is a Double by default.

3. Step 3: Check options

   var score: Double = 95.5 uses var and Double with correct value. Others either use val, wrong type, or wrong value type.

4. Final Answer:

   var score: Double = 95.5 -> Option A

5. Quick Check:

   var + Double for changeable decimal [OK]

Hint: Use var for changeable, Double for decimals [OK]

Common Mistakes:

• Using val when variable should change
• Assigning decimal to Int type
• Putting string value for numeric type