Boolean type and logical operators in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using logical operators?

Consider the following Kotlin code snippet. What will it print?

Kotlin

fun main() {
    val a = true
    val b = false
    val c = a && !b || b
    println(c)
}

A true

B false

C Compilation error

D Runtime exception

💡 Hint

Remember that !b means 'not b', and && has higher precedence than ||.

The expression evaluates as (a && (!b)) || b. Since a is true and b is false, !b is true. So true && true is true, and true || false is true.

❓ Predict Output

intermediate

What does this Kotlin code print with mixed logical operators?

Analyze the output of this Kotlin program:

Kotlin

fun main() {
    val x = false
    val y = true
    val result = x || y && false
    println(result)
}

A true

B false

C Compilation error

D Runtime exception

💡 Hint

&& has higher precedence than || in Kotlin.

The expression is x || (y && false). y && false is false, so x || false is false || false, which is false.

🔧 Debug

advanced

What error does this Kotlin code raise?

Examine this Kotlin snippet and identify the error it produces when compiled or run:

Kotlin

fun main() {
    val a = true
    val b = false
    val c = a && b ||
    println(c)
}

A No error, prints false

B TypeError

C Unresolved reference error

D SyntaxError

💡 Hint

Look carefully at the expression assigned to c.

The expression ends abruptly with '||' without a right-hand operand, causing a syntax error.

❓ Predict Output

advanced

What is the output of this Kotlin code using logical negation and equality?

What will this Kotlin program print?

Kotlin

fun main() {
    val a = true
    val b = false
    val c = !(a == b) && (a || b)
    println(c)
}

A Compilation error

B false

C true

D Runtime exception

💡 Hint

Evaluate the equality first, then apply negation and logical operators.

a == b is false, so !(false) is true. a || b is true. true && true is true.

🧠 Conceptual

expert

How many items are in the resulting list after filtering with logical operators?

Given this Kotlin code, how many elements does the list 'filtered' contain?

Kotlin

fun main() {
    val numbers = listOf(1, 2, 3, 4, 5, 6)
    val filtered = numbers.filter { it % 2 == 0 && it > 3 || it == 1 }
    println(filtered.size)
}

A 4

B 3

C 2

D 5

💡 Hint

Remember that && has higher precedence than || in Kotlin filter conditions.

The filter condition is (it % 2 == 0 && it > 3) || it == 1. Even numbers greater than 3 are 4 and 6, plus 1. So filtered list is [1,4,6], size 3.

Practice

1. What type of value does the Kotlin Boolean type store?

easy

A. Decimal numbers

B. True or false values

C. Text strings

D. Numbers only

Solution

1. Step 1: Understand the Boolean type

   The Boolean type in Kotlin is designed to hold only two possible values: true or false.

2. Step 2: Identify the correct value type

   Since Boolean stores true or false, it cannot store numbers or text strings.

3. Final Answer:

   True or false values -> Option B

4. Quick Check:

   Boolean = true/false [OK]

Hint: Boolean means true or false only [OK]

Common Mistakes:

• Thinking Boolean stores numbers
• Confusing Boolean with String
• Assuming Boolean can hold multiple values

2. Which of the following is the correct syntax for the logical AND operator in Kotlin?

easy

A. &&

B. ||

C. and

D. !

Solution

1. Step 1: Recall Kotlin logical operators

   Kotlin uses && for logical AND, || for OR, and ! for NOT.

2. Step 2: Match operator to AND

   The operator && combines two Boolean expressions and returns true only if both are true.

3. Final Answer:

   && -> Option A

4. Quick Check:

   AND operator = && [OK]

Hint: AND is double ampersand && in Kotlin [OK]

Common Mistakes:

• Using || instead of && for AND
• Writing 'and' as a keyword
• Confusing NOT (!) with AND

3. What is the output of the following Kotlin code?

val a = true
val b = false
println(a || b && !b)

medium

A. false

B. null

C. true

D. Compilation error

Solution

1. Step 1: Evaluate NOT operator

   !b means !false, which is true.

2. Step 2: Evaluate AND operator

   b && !b means false && true, which is false.

3. Step 3: Evaluate OR operator

   a || (result of AND) means true || false, which is true.

4. Final Answer:

   true -> Option C

5. Quick Check:

   Logical operators follow precedence: !, &&, then || [OK]

Hint: Remember operator precedence: ! > && > || [OK]

Common Mistakes:

• Ignoring operator precedence
• Evaluating OR before AND
• Confusing !b value

4. Identify the error in this Kotlin code snippet:

val x = true
val y = false
val result = x & y
println(result)

medium

A. Using single & instead of && for logical AND

B. Missing semicolon after println

C. Boolean variables cannot be assigned like this

D. No error, code runs fine

Solution

1. Step 1: Check operator usage

   In Kotlin, logical AND uses &&, not single &. Single & is bitwise AND, not for Booleans.

2. Step 2: Understand error cause

   Using & with Booleans causes a type mismatch error.

3. Final Answer:

   Using single & instead of && for logical AND -> Option A

4. Quick Check:

   Logical AND = &&, not & [OK]

Hint: Use && for Boolean AND, not single & [OK]

Common Mistakes:

• Using & instead of && for logical AND
• Thinking semicolon is required
• Assuming Boolean assignment is invalid

5. Given the Kotlin variables:

val isSunny = false
val hasUmbrella = true
val isWarm = true

Which expression correctly checks if it is either sunny or warm, and you have an umbrella if not sunny?

hard

A. isSunny && isWarm || hasUmbrella

B. (isSunny || isWarm) && hasUmbrella

C. (isSunny && hasUmbrella) || isWarm

D. isSunny || (isWarm && hasUmbrella)

Solution

1. Step 1: Understand the condition

   We want true if it is sunny OR if it is warm AND you have an umbrella when it is not sunny.

2. Step 2: Translate condition to logic

   The expression should be: isSunny OR (isWarm AND hasUmbrella). This means if sunny, no umbrella needed; if not sunny, then warm and umbrella required.

3. Final Answer:

   isSunny || (isWarm && hasUmbrella) -> Option D

4. Quick Check:

   Use parentheses to group AND inside OR [OK]

Hint: Group AND inside OR with parentheses for correct logic [OK]

Common Mistakes:

• Ignoring parentheses changing logic
• Assuming umbrella needed when sunny
• Mixing AND and OR without grouping