Logical operators (&&, ||, !) in Ruby - Mini Project: Build & Apply

Using Logical Operators in Ruby

📖 Scenario: You are helping a small shop decide if a customer qualifies for a special discount. The shop has simple rules based on the customer's age and membership status.

🎯 Goal: Build a Ruby program that uses logical operators && and || to check if a customer qualifies for a discount.

📋 What You'll Learn

Create variables with exact names and values as instructed

Use logical operators && and || exactly as shown

Print the exact output string as instructed

💡 Why This Matters

🌍 Real World

Stores and businesses often use simple rules to decide if customers get discounts or special offers based on their age or membership.

💼 Career

Understanding logical operators is essential for writing conditions in programs, which is a key skill for any software developer.

1

Create customer data variables

Create a variable called age and set it to 25. Create another variable called is_member and set it to true.

Ruby

# Create variables 'age' and 'is_member' with given values
# Your code here

Hint

Use = to assign values. For is_member, use true without quotes.

2

Create discount eligibility rules

Create a variable called is_senior and set it to false. Create a variable called min_age and set it to 60.

Ruby

age = 25
is_member = true
# Create variables 'is_senior' and 'min_age' with given values
# Your code here

Hint

Remember to use false without quotes for boolean false.

3

Use logical operators to check discount eligibility

Create a variable called qualifies_for_discount that is true if the customer is a member and their age is less than min_age, or if they are a senior. Use && and || operators exactly as shown.

Ruby

age = 25
is_member = true
is_senior = false
min_age = 60
# Create 'qualifies_for_discount' using logical operators
# Your code here

Hint

Use parentheses to group conditions clearly. qualifies_for_discount should be true if either condition is met.

4

Print the discount eligibility result

Print the exact text "Discount eligibility: true" or "Discount eligibility: false" depending on the value of qualifies_for_discount. Use puts and string interpolation with #{}.

Ruby

age = 25
is_member = true
is_senior = false
min_age = 60
qualifies_for_discount = (is_member && age < min_age) || is_senior
# Print the discount eligibility result below
# Your code here

Hint

Use puts and "Discount eligibility: #{qualifies_for_discount}" to print the result.

Practice

1. What does the Ruby logical operator && do?

easy

A. Checks if two values are equal

B. Returns true if at least one condition is true

C. Reverses the truth value of a condition

D. Returns true only if both conditions are true

Solution

1. Step 1: Understand the meaning of &&

   The && operator means 'and' in Ruby, so it returns true only if both sides are true.

2. Step 2: Compare with other operators

   || returns true if one or both are true, and ! reverses truth. Equality checks with ==.

3. Final Answer:

   Returns true only if both conditions are true -> Option D

4. Quick Check:

   && means AND = D [OK]

Hint: && means both must be true to get true [OK]

Common Mistakes:

• Confusing && with ||
• Thinking && reverses values
• Mixing && with equality operator

2. Which of the following is the correct way to write a NOT operation in Ruby?

easy

A. !x

B. ~x

C. not x

D. x != true

Solution

1. Step 1: Identify Ruby's NOT operator syntax

   Ruby uses ! before a value to reverse its truth value.

2. Step 2: Check other options

   not x is valid but less common; ~x is bitwise NOT; x != true is a comparison, not logical NOT.

3. Final Answer:

   !x -> Option A

4. Quick Check:

   Logical NOT = C [OK]

Hint: Use ! before a value to reverse true/false [OK]

Common Mistakes:

• Using ~ instead of ! for logical NOT
• Confusing != with NOT operator
• Using 'not' keyword instead of !

3. What is the output of this Ruby code?

puts (true || false) && !false

medium

A. nil

B. false

C. true

D. SyntaxError

Solution

1. Step 1: Evaluate inside parentheses

   true || false is true because at least one side is true.

2. Step 2: Evaluate the NOT operator

   !false is true because NOT false is true.

3. Step 3: Evaluate the AND operator

   Now we have true && true, which is true.

4. Final Answer:

   true -> Option C

5. Quick Check:

   (true || false) && !false = A [OK]

Hint: Evaluate parentheses, then !, then && [OK]

Common Mistakes:

• Evaluating && before ||
• Forgetting to apply ! operator
• Assuming false because of || false

4. Find the error in this Ruby code snippet:

if !true || false
  puts "Yes"
else
  puts "No"
end

medium

A. No error; code runs and prints "No"

B. The ! operator cannot be used with true

C. The || operator should be && here

D. Missing parentheses around !true

Solution

1. Step 1: Check syntax of logical operators

   Using ! with true is valid and reverses it to false. The || operator is also valid here.

2. Step 2: Evaluate the condition

   !true is false, so condition is false || false, which is false. The else branch runs printing "No".

3. Step 3: Confirm no syntax errors

   The code syntax is correct and will run without errors.

4. Final Answer:

   No error; code runs and prints "No" -> Option A

5. Quick Check:

   Logical operators used correctly = B [OK]

Hint: !true is valid; check logic, not syntax [OK]

Common Mistakes:

• Thinking !true is invalid
• Confusing || with &&
• Expecting syntax error without parentheses

5. You want to check if a variable x is NOT between 10 and 20 inclusive in Ruby. Which condition correctly uses logical operators?

hard

A. !(x >= 10 && x <= 20)

B. x < 10 || x > 20

C. x <= 10 && x >= 20

D. !(x < 10 || x > 20)

Solution

1. Step 1: Understand the range condition

   Being between 10 and 20 inclusive means x >= 10 && x <= 20.

2. Step 2: Find the NOT of the range

   The NOT of being between 10 and 20 is being less than 10 OR greater than 20, so x < 10 || x > 20.

3. Step 3: Check options

   !(x >= 10 && x <= 20) negates the range but is correct logically; x < 10 || x > 20 directly expresses the NOT condition without negation. x <= 10 && x >= 20 is impossible (x can't be both <=10 and >=20). !(x < 10 || x > 20) negates the NOT condition, so it's the original range.

4. Final Answer:

   x < 10 || x > 20 -> Option B

5. Quick Check:

   NOT between 10 and 20 = A [OK]

Hint: NOT between means less than OR greater than [OK]

Common Mistakes:

• Using AND instead of OR for NOT condition
• Confusing negation placement
• Choosing impossible conditions