Boolean type and logical operators in Kotlin - Mini Project: Build & Apply

Boolean type and logical operators

📖 Scenario: You are creating a simple program to check if a person is eligible for a discount based on their age and membership status.

🎯 Goal: Build a Kotlin program that uses Boolean variables and logical operators to decide if a person gets a discount.

📋 What You'll Learn

Create Boolean variables to represent conditions

Use logical operators && (AND), || (OR), and ! (NOT)

Print the final eligibility result

💡 Why This Matters

🌍 Real World

Many apps check user eligibility for offers or access using true/false conditions combined with AND, OR, and NOT.

💼 Career

Understanding Boolean logic is essential for programming decisions, validations, and controlling program flow.

1

Create Boolean variables for age and membership

Create two Boolean variables called isAdult and isMember. Set isAdult to true and isMember to false.

Kotlin

# Your code here

Hint

Use val to create Boolean variables and assign true or false.

2

Create a Boolean variable for discount eligibility

Add a Boolean variable called hasDiscount that is true if the person is an adult AND a member. Use the && operator with isAdult and isMember.

Kotlin

fun main() {
    val isAdult = true
    val isMember = false
    
    // Create hasDiscount using isAdult && isMember
    // Your code here
}

Hint

Use val hasDiscount = isAdult && isMember to combine the two conditions.

3

Add a condition for senior discount using OR operator

Create a Boolean variable called isSenior and set it to true. Then update hasDiscount to be true if the person is an adult AND a member OR if the person is a senior. Use || operator.

Kotlin

fun main() {
    val isAdult = true
    val isMember = false
    
    val hasDiscount = isAdult && isMember
    
    // Create isSenior and update hasDiscount
    // Your code here
}

Hint

Use parentheses to group isAdult && isMember before OR isSenior.

4

Print the discount eligibility result

Write a println statement to display the value of hasDiscount.

Kotlin

fun main() {
    val isAdult = true
    val isMember = false
    
    val isSenior = true
    val hasDiscount = (isAdult && isMember) || isSenior
    
    // Print hasDiscount
    // Your code here
}

Hint

Use println(hasDiscount) to show the result.

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