Logical operators in C++ - Mini Project: Build & Apply

Logical Operators Practice

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

🎯 Goal: Build a program that uses logical operators to decide if a person qualifies for the discount.

📋 What You'll Learn

Create variables for age and membership status

Create a variable for minimum age to qualify

Use logical operators to check if the person is both old enough and a member

Print the eligibility result

💡 Why This Matters

🌍 Real World

Checking eligibility for discounts or offers based on multiple conditions is common in stores, websites, and apps.

💼 Career

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

1

Create variables for age and membership status

Create an int variable called age and set it to 25. Create a bool variable called isMember and set it to true.

C++

// Your code here

Hint

Use int for numbers and bool for true/false values.

2

Create a variable for minimum age to qualify

Create an int variable called minAge and set it to 18.

C++

int age = 25;
bool isMember = true;
// Your code here

Hint

This variable will hold the minimum age required for the discount.

3

Use logical operators to check eligibility

Create a bool variable called isEligible that is true only if age is greater than or equal to minAge and isMember is true. Use the logical AND operator &&.

C++

int age = 25;
bool isMember = true;
int minAge = 18;
// Your code here

Hint

Use parentheses to group conditions clearly.

4

Print the eligibility result

Use std::cout to print "Eligible for discount: " followed by the value of isEligible. Include #include <iostream> and use std::boolalpha to print true or false instead of 1 or 0.

C++

#include 

int main() {
int age = 25;
bool isMember = true;
int minAge = 18;
bool isEligible = (age >= minAge) && isMember;
// Your code here
return 0;
}

Hint

Remember to include #include <iostream> and use std::boolalpha to print true or false.

Practice

1. Which logical operator in C++ means "both conditions must be true"?

easy

A. &&

B. ||

C. !

D. &

Solution

1. Step 1: Understand the meaning of logical AND

   The operator that requires both conditions to be true is called logical AND.

2. Step 2: Identify the C++ symbol for logical AND

   In C++, logical AND is represented by &&.

3. Final Answer:

   && -> Option A

4. Quick Check:

   Both true = true means && [OK]

Hint: && means both true; || means one true [OK]

Common Mistakes:

• Confusing & (bitwise AND) with && (logical AND)
• Thinking || means both true
• Mixing ! with AND or OR

2. Which of the following is the correct syntax to negate a boolean variable flag in C++?

easy

A. !flag = flag;

B. flag = flag!;

C. flag != flag;

D. flag = !flag;

Solution

1. Step 1: Recall the negation operator syntax

   The negation operator ! is placed before the variable to flip its value.

2. Step 2: Check correct assignment syntax

   To update flag to its negation, write flag = !flag; which is valid C++ syntax.

3. Final Answer:

   flag = !flag; -> Option D

4. Quick Check:

   Negate with ! before variable [OK]

Hint: Put ! before variable to negate [OK]

Common Mistakes:

• Placing ! after variable (invalid syntax)
• Using != which means not equal
• Trying to assign to !flag (not a variable)

3. What is the output of this C++ code?

bool a = true;
bool b = false;
if (a || b) {
  std::cout << "Yes";
} else {
  std::cout << "No";
}

medium

A. Yes

B. No

C. true

D. false

Solution

1. Step 1: Evaluate the logical OR condition

   a is true, b is false, so a || b is true because at least one is true.

2. Step 2: Determine which branch runs

   Since the condition is true, the if block runs and prints "Yes".

3. Final Answer:

   Yes -> Option A

4. Quick Check:

   true || false = true [OK]

Hint: || is true if any side is true [OK]

Common Mistakes:

• Thinking both must be true for ||
• Confusing output with boolean literals
• Ignoring that std::cout prints strings

4. Find the error in this C++ code snippet:

bool x = true;
bool y = false;
if (x & y) {
  std::cout << "True";
} else {
  std::cout << "False";
}

medium

A. Incorrect use of std::cout

B. Missing semicolon after bool declarations

C. Using & instead of && in if condition

D. Variables x and y not initialized

Solution

1. Step 1: Identify the operator used in condition

   The code uses & which is bitwise AND, not logical AND.

2. Step 2: Explain why && is needed

   For boolean logic in conditions, && should be used to combine true/false values.

3. Final Answer:

   Using & instead of && in if condition -> Option C

4. Quick Check:

   Logical AND needs && not & [OK]

Hint: Use && for logic, & is bitwise [OK]

Common Mistakes:

• Confusing bitwise & with logical &&
• Assuming & works like && in conditions
• Ignoring operator precedence differences

5. Given int a = 5; and int b = 10;, which condition correctly checks if a is less than 10 AND b is greater than 5?

hard

A. if (a < 10 || b > 5)

B. if (a < 10 && b > 5)

C. if (!(a < 10) && !(b > 5))

D. if (a > 10 && b < 5)

Solution

1. Step 1: Understand the condition requirements

   We want both: a less than 10 AND b greater than 5.

2. Step 2: Match condition with logical AND

   Logical AND (&&) combines both conditions to be true simultaneously.

3. Final Answer:

   if (a < 10 && b > 5) -> Option B

4. Quick Check:

   Both true means && [OK]

Hint: Use && to require both conditions true [OK]

Common Mistakes:

• Using || which means either condition true
• Negating conditions incorrectly
• Swapping comparison operators