C#: Logical Operators

C# provides three logical operators, These are &&(AND), || (OR), and !(NOT)

Logical AND is also called Conditional AND

Logical OR is also called Conditional OR

Logical AND, OR are called Short circuit operators, will see why these are called short circuit soon.

Logical AND Operator

Operand1	Operand2	Evaluates To
TRUE	TRUE	TRUE
TRUE	FALSE	FALSE
FALSE	TRUE	FALSE
FALSE	FALSE	FALSE

Program.cs

using System;

class Program
{
    static void Main(string[] args)
    {
        bool operand1 = true;
        bool operand2 = true;

        Console.WriteLine("operand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 && operand2 = {0}", (operand1 && operand2));

        operand1 = true;
        operand2 = false;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 && operand2 = {0}",(operand1 && operand2));

        operand1 = false;
        operand2 = true;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 && operand2 = {0}", (operand1 && operand2));

        operand1 = false;
        operand2 = false;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 && operand2 = {0}", (operand1 && operand2));
    }
}

Output

operand1 = True
operand2 = True
operand1 && operand2 = True

operand1 = True
operand2 = False
operand1 && operand2 = False

operand1 = False
operand2 = True
operand1 && operand2 = False

operand1 = False
operand2 = False
operand1 && operand2 = False

Why Logical AND is called short circuit operator?

Since if the first statement in the expression evaluates to false, then java won't evaluate the entire expression. So Logical AND is called short circuit AND.

Program.cs

using System;

class Program
{
    static void Main(string[] args)
    {
        int a = 10, b = 21;

        if ((a > b) && (a++ > b))
        {
            Console.WriteLine("This statement not evaluated");
        }
        Console.WriteLine("a is not incremented " + a);

        if ((a < b) && (a++ < b))
        {
            Console.WriteLine("This statement is evaluated");
        }
        Console.WriteLine("a is incremented " + a);
    }
}

Output

a is not incremented 10

This statement is evaluated

a is incremented 11

Observation

In the expression (a>b) && (a++ > b), a>b is false, so && operator won't evaluate second statement in the expression, so a is not incremented.

Logical OR Operator

Operand1	Operand2	Evaluates To
TRUE	TRUE	TRUE
TRUE	FALSE	TRUE
FALSE	TRUE	TRUE
FALSE	FALSE	FALSE

As shown in the above table, || operator returns true if any of the operand evaluates to true, otherwise returns false.

Program.cs

using System;

class Program
{
    static void Main(string[] args)
    {
        bool operand1 = true;
        bool operand2 = true;

        Console.WriteLine("operand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 || operand2 = {0}", (operand1 || operand2));

        operand1 = true;
        operand2 = false;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 || operand2 = {0}", (operand1 || operand2));

        operand1 = false;
        operand2 = true;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 || operand2 = {0}", (operand1 || operand2));

        operand1 = false;
        operand2 = false;
        Console.WriteLine("\noperand1 = {0}", operand1);
        Console.WriteLine("operand2 = {0}", operand2);
        Console.WriteLine("operand1 || operand2 = {0}", (operand1 || operand2));

    }
}

Output

operand1 = True
operand2 = True
operand1 || operand2 = True

operand1 = True
operand2 = False
operand1 || operand2 = True

operand1 = False
operand2 = True
operand1 || operand2 = True

operand1 = False
operand2 = False
operand1 || operand2 = False

Why Logical OR is called short circuit operator?

Since if the first statement evaluates to true, then java won't evaluates the entire expression. So Logial OR is called short circuit OR.

Program.cs

using System;

class Program
{
    static void Main(string[] args)
    {
        int a = 10, b = 21;

        if ((a < b) || (a++ < b))
        {
            Console.WriteLine("This statement evaluated");
        }
        Console.WriteLine("a is not incremented " + a);

        if ((a > b) || (a++ > b))
        {
            Console.WriteLine("This statement is evaluated");
        }
        Console.WriteLine("a is incremented " + a);

    }
}

Output

This statement evaluated

a is not incremented 10

a is incremented 11

Logical (!)NOT operator

Operand	Evaluates To
FALSE	TRUE
TRUE	FALSE

        

If the operand is FALSE, ! Operator evaluates it to TRUE

If the operand is TRUE, ! Operator evaluates it to FALSE.

Program.cs

using System;

class Program
{
    static void Main(string[] args)
    {
        bool a = true;
        Console.WriteLine("a = {0}, !a = {1}", a, !a);

        a = false;
        Console.WriteLine("a = {0}, !a = {1}", a, !a);
    }
}

Output

operand1 = True
operand2 = True
operand1 || operand2 = True

operand1 = True
operand2 = False
operand1 || operand2 = True

operand1 = False
operand2 = True
operand1 || operand2 = True

operand1 = False
operand2 = False
operand1 || operand2 = False

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