G-Fact 19 (Logical and Bitwise Not Operators on Boolean)

1.7

Most of the languages including C, C++, Java and Python provide the boolean type that can be either set to False or True.

Consider below programs that use Logical Not (or !) operator on boolean.

Python

# A Python program that uses Logical Not or ! on boolean
a = not True
b = not False
print a
print b
# Output: False
#         True

C/C++

// A C/C++ program that uses Logical Not or ! on boolean
#include <stdio.h>
#include <stdbool.h>

int main()
{
    bool a = 1, b = 0;
    a = !a;
    b = !b;
    printf("%d\n%d", a, b);
    return 0;
}
// Output: 0
//         1

Java

// A Java program that uses Logical Not or ! on boolean
import java.io.*;

class GFG
{
    public static void main (String[] args)
    {
        boolean a = true, b = false;
        System.out.println(!a);
        System.out.println(!b);
    }
}
// Output: False
//         True

The outputs of above programs are as expected, but the outputs following programs may not be as expected if we have not used Bitwise Not (or ~) operator before.

Python

# A Python program that uses Bitwise Not or ~ on boolean
a = True
b = False
print ~a
print ~b

C/C++

// C/C++ program that uses Bitwise Not or ~ on boolean
#include <bits/stdc++.h>
using namespace std;
int main()
{
    bool a = true, b = false;
    cout << ~a << endl << ~b;
    return 0;
}


Output:

-2
-1

Reason: The bitwise not operator ~ returns the complement of a number i.e., it switches each 1 to 0 and each 0 to 1. Booleans True and False have values 1 and 0 respectively.

˜being the bitwise not operator,

  • The expression “˜True” returns bitwise inverse of 1.
  • The expression “˜False” returns bitwise inverse of 0.

 

Java doesn’t allow ~ operator to be applied on boolean values. For example, the below program produces compiler error.

// A Java program that uses Bitwise Not or ~ on boolean
import java.io.*;

class GFG
{
    public static void main (String[] args)
    {
        boolean a = true, b = false;
        System.out.println(~a);
        System.out.println(~b);
    }
}

Output:

6: error: bad operand type boolean for unary operator '~'
		System.out.println(~a);
		                   ^
7: error: bad operand type boolean for unary operator '~'
		System.out.println(~b);
		                   ^
2 errors

Conclusion:
“Logical not or !” is meant for boolean values and “bitwise not or ~” is for integers. Languages like C/C++ and python do auto promotion of boolean to integer type when an integer operator is applied. But Java doesn’t do it.

This article is contributed by Arpit Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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