Logical operators in C++ tutorial

Logical operators in C++ are used to combine or invert boolean expressions. They play a critical role in control flow, allowing multiple conditions to be evaluated together.

Logical operators evaluate to a boolean value (true or false) and are commonly used in if statements, loops, and other conditional expressions.

List of Logical Operators in C++

1. Logical AND (&&)

The logical AND operator (&&) returns true only if both operands are true. If either operand is false, the entire expression evaluates to false.

#include <iostream>
using namespace std;

int main() {
    int age = 20;
    bool hasID = true;

    if (age >= 18 && hasID) {
        cout << "You are allowed entry." << endl;
    } else {
        cout << "Entry denied." << endl;
    }

    return 0;
}

Explanation:

• The expression age >= 18 && hasID checks if age is 18 or older and hasID is true.
• If both conditions are true, “You are allowed entry” is printed.

Output:

You are allowed entry.

2. Logical OR (||)

The logical OR operator (||) returns true if at least one of the operands is true. If both operands are false, the expression evaluates to false.

#include <iostream>
using namespace std;

int main() {
    int temperature = 35;
    bool isRaining = true;

    if (temperature > 30 || isRaining) {
        cout << "Stay indoors." << endl;
    } else {
        cout << "You can go outside." << endl;
    }

    return 0;
}

Explanation:

• The expression temperature > 30 || isRaining checks if the temperature is over 30 or if it's raining.
• If either condition is true, “Stay indoors” is printed.

Output:

Stay indoors.

3. Logical NOT (!)

The logical NOT operator (!) inverts the boolean value of the operand. If the operand is true, it becomes false; if it's false, it becomes true.

#include <iostream>
using namespace std;

int main() {
    bool isAvailable = false;

    if (!isAvailable) {
        cout << "Item is not available." << endl;
    } else {
        cout << "Item is available." << endl;
    }

    return 0;
}

Explanation:

• !isAvailable inverts isAvailable. Since isAvailable is false, !isAvailable is true.
• “Item is not available” is printed if isAvailable is false.

Output:

Item is not available.

4. Combining Logical Operators

Logical operators can be combined to form more complex conditions. Use parentheses to clarify the order of evaluation.

#include <iostream>
using namespace std;

int main() {
    int age = 22;
    bool hasID = true;
    bool withParent = false;

    if ((age >= 18 && hasID) || withParent) {
        cout << "You are allowed entry." << endl;
    } else {
        cout << "Entry denied." << endl;
    }

    return 0;
}

Explanation:

• The expression (age >= 18 && hasID) || withParent evaluates to true if the person is 18 or older and has an ID, or if they are with a parent.
• Parentheses group conditions, ensuring age >= 18 && hasID is evaluated together.

Output:

You are allowed entry.

5. Using Logical Operators in Conditional Statements

Logical operators are often used in if statements to make decisions based on multiple conditions.

#include <iostream>
using namespace std;

int main() {
    int score = 85;
    int attendance = 90;

    if (score >= 80 && attendance >= 75) {
        cout << "You passed the course." << endl;
    } else {
        cout << "You did not pass the course." << endl;
    }

    return 0;
}

Explanation:

• score >= 80 && attendance >= 75 checks if both score and attendance meet the requirements for passing.

Output:

You passed the course.

6. Using Logical Operators in Loops

Logical operators can control loop execution based on multiple conditions.

#include <iostream>
using namespace std;

int main() {
    int count = 0;

    while (count < 10 && count % 2 == 0) {
        cout << "Count: " << count << endl;
        count += 2;
    }

    return 0;
}

Explanation:

• The loop runs while count is less than 10 and even (count % 2 == 0).
• When count reaches 10, the loop stops.

Output:

Count: 0
Count: 2
Count: 4
Count: 6
Count: 8

7. Logical Operators with User Input

Logical operators can validate multiple conditions with user input.

#include <iostream>
using namespace std;

int main() {
    int age;
    char gender;

    cout << "Enter age: ";
    cin >> age;
    cout << "Enter gender (M/F): ";
    cin >> gender;

    if (age >= 18 && (gender == 'M' || gender == 'F')) {
        cout << "Eligible for the program." << endl;
    } else {
        cout << "Not eligible for the program." << endl;
    }

    return 0;
}

Explanation:

• age >= 18 && (gender == ‘M' || gender == ‘F') checks if age is at least 18 and gender is either M or F.

Sample Output:

Enter age: 20
Enter gender (M/F): M
Eligible for the program.

8. Short-Circuit Evaluation in Logical Operators

C++ uses short-circuit evaluation for && and ||. This means that if the result of the logical expression can be determined from the first operand, the second operand is not evaluated.

#include <iostream>
using namespace std;

bool checkAge(int age) {
    cout << "Checking age... ";
    return age >= 18;
}

bool checkID(bool hasID) {
    cout << "Checking ID... ";
    return hasID;
}

int main() {
    int age = 20;
    bool hasID = true;

    if (checkAge(age) && checkID(hasID)) {
        cout << "Access granted." << endl;
    } else {
        cout << "Access denied." << endl;
    }

    return 0;
}

Explanation:

• If checkAge(age) returns false, checkID(hasID) is not called because the result of && would already be false.

Output:

Checking age... Access granted.

9. Logical NOT (!) with Relational Operators

The logical NOT operator (!) is often used to simplify conditions in if statements by inverting a relational expression.

#include <iostream>
using namespace std;

int main() {
    bool isStudent = true;
    bool isMember = false;

    if (!isStudent && !isMember) {
        cout << "You need to be a student or a member for access." << endl;
    } else {
        cout << "Access granted." << endl;
    }

    return 0;
}

Explanation:

• !isStudent && !isMember checks if neither isStudent nor isMember is true.

Output:

Access granted.

10. Summary Table of Logical Operators in C++

Complete Example: Combining Logical Operators

This example demonstrates a complete program using logical operators to evaluate multiple conditions for entry eligibility based on age, parental supervision, and membership status.

#include <iostream>
using namespace std;

int main() {
    int age;
    bool isMember;
    bool withParent;

    cout << "Enter age: ";
    cin >> age;
    cout << "Are you a member? (1 for yes, 0 for no): ";
    cin >>

 isMember;
    cout << "Are you with a parent? (1 for yes, 0 for no): ";
    cin >> withParent;

    if ((age >= 18 || withParent) && isMember) {
        cout << "Entry granted." << endl;
    } else {
        cout << "Entry denied." << endl;
    }

    return 0;
}

Explanation:

• The condition (age >= 18 || withParent) && isMember checks if the user is 18 or older or with a parent and is a member.
• If the condition is met, “Entry granted” is printed.

Sample Output:

Enter age: 16
Are you a member? (1 for yes, 0 for no): 1
Are you with a parent? (1 for yes, 0 for no): 1
Entry granted.

Logical operators in C++ enable complex condition handling and are essential for controlling program flow.