Logical Operators

Logical Operators can be used for combining two logical expressions or logical values. Following are the three logical operators:

Operator	Operation
&&	AND
\|\|	OR
!	NOT

Note
An operand refers to a value or expression that is used as an input for an operator in a statement or expression. For-example in the expression 1 + 2, the values 1 and 2 are operands. In the case of logical operators, an operand is always a boolean expression or value.

The AND (&&) operator takes two operands and returns true only if both the operands are true. It is demonstrated by the following code:

main


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using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			Console.WriteLine(true && true); // Output: True
			Console.WriteLine(true && false); // Output: False
			Console.WriteLine(false && true); // Output: False
			Console.WriteLine(false && false); // Output: False
        }
    }
}

Instead of directly using the true and false literals (values), we commonly use expressions:

main


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using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			/* A program to check if the variable `value` 
            is in the range specified by `range_start` 
            and `range_end` variables.*/
			int value = 7;
			int range_start = 0;
			int range_end = 10;
			Console.WriteLine(range_start < value && value < range_end); // Output: True
        }
    }
}

The OR (||) operator returns true if any one of the operands is true:

main


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using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			Console.WriteLine(true || true); // Output: True
			Console.WriteLine(true || false); // Output: True
			Console.WriteLine(false || true); // Output: True
			Console.WriteLine(false || false); // Output: False
        }
    }
}

Following is an example which uses the OR (||) operator:

main


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using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int val1 = 5;
			int val2 = 7;
			int val3 = 9;

			Console.WriteLine(val2 > val1 || val2 > val3); // Output: True
        }
    }
}

The NOT (!) operator simply negates (inverts) the logical expression or logical value. So if an expression returns true, it changes it into false.

main


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using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			Console.WriteLine(!true); // Output: False
			Console.WriteLine(!false); // Output: True

			// We need to enclose expressions in brackets () before negating them
			Console.WriteLine(!(5 < 0)); // Output: True
			Console.WriteLine(!(0 < 5 && 5 < 10)); // Output: False
        }
    }
}

Everything was clear?

Section 3. Chapter 2