C++ Logical (&&, ||, !) Operator Overloading

Prerequisites: 

• Operators
• Operator Overloading

Logical operators are used for combining two or more conditions or constraints or to complement the evaluation of the original condition in consideration. The result returns a Boolean value, i.e., true or false. In C++, there are 3 logical operators: 

• Logical AND (&&): This operator returns true only if all the operands are true or non-zero.
• Logical OR ( || ): This operator returns true if either of the operands is true or non-zero.
• Logical NOT ( ! ): This operator returns true if the operand is false or zero and vice-versa.

To use a logical operator on user-defined data type operator overloading is needed. Redefining the meaning of operators really does not change their original meaning, instead, they have been given additional meaning along with their existing ones.

Example 1:

C++

// C++ program for ! Operator overloading

#include <iostream>
using namespace std;
class A {
private:
    int a;

public:
    // parameterized constructor
    A(int l) { a = l; }

    // This is automatically called
    // when ! operator is
    // used with object
    bool operator!()
    {
        a = !a;
        if (a)
            return true;
        else
            return false;
    }
};

// Driver Code
int main()
{
    // Assigning by overloading constructor
    A a1(7), a2(0);

    // Overloading ! Operator
    if (!a1) {
        cout << "a1 value is zero" << endl;
    }
    else {
        cout << "a1 value is non-zero" << endl;
    }

    if (!a2) {
        cout << "a2 value is zero" << endl;
    }
    else {
        cout << "a2 value is non-zero" << endl;
    }
}

Output

a1 value is non-zero
a2 value is zero

Example 2: Overloading AND (&&) Logical Operator

C++

// C++ program for && Operator overloading

#include <iostream>
using namespace std;
class A {
private:
    int value;

public:
    // Non-parameterized constructor
    A() {}
    // parameterized constructor
    A(int l) { value = l; }

    // This is automatically called
    // when '&&' operator is
    // used between a1 and a2.
    A operator&&(const A& a)
    {
        A obj;
        obj.value = value && a.value;
        return obj;
    }

    // method to display result
    void result()
    {
        if (value)
            cout << "Both value is non zero" << endl;
        else
            cout << "Any one or both value is equal to zero"
                 << endl;
    }
};

// Driver Code
int main()
{
    // Assigning by overloading constructor
    A a1(95), a2(78);
    A a3;

    // overloading && operator and storing the result in a3
    // a3=a1.&&(a2);
    a3 = a1 && a2;
    a3.result();
    return 0;
}

Output

Both value is non zero

Example 3: Overloading OR (||) Operator

C++

// C++ program for || Operator overloading

#include <iostream>
using namespace std;
class A {
private:
    int value;

public:
    // Non-parameterized constructor
    A() {}
    // parameterized constructor
    A(int l) { value = l; }

    // This is automatically called
    // when '||' operator is
    // used between a1 and a2.
    A operator||(const A& a)
    {
        A obj;
        obj.value = value || a.value;
        return obj;
    }

    // method to display result
    void result()
    {
        if (value)
            cout << "Any one or both value is non zero"
                 << endl;
        else
            cout << "Both value is equal to zero" << endl;
    }
};

// Driver Code
int main()
{
    // Assigning by overloading constructor
    A a1(95), a2(0);
    A a3;

    // overloading || operator and storing the result in a3
    // a3=a1.||(a2);
    a3 = a1 || a2;
    a3.result();
    return 0;
}

Output

Any one or both value is non zero