C++ not Keyword

The not keyword in C++ is an alternative representation of the logical NOT operator (!).

It is part of the set of alternative tokens introduced to make code more readable and writable, especially in non-English keyboard layouts. The not keyword performs the same operation as !: it inverts the truth value of a Boolean expression.

Syntax

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not expression
not
The keyword that inverts the truth value of the expression.
expression
The Boolean expression to be negated.

Examples

Example 1: Basic Use of not Keyword

This example demonstrates the equivalence of not and the logical NOT operator (!).

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#include <iostream>
using namespace std;

int main() {
    bool isTrue = true;

    cout << "Using ! operator: " << (!isTrue) << endl;
    cout << "Using not keyword: " << (not isTrue) << endl;

    return 0;
}

Output:

Using ! operator: 0
Using not keyword: 0

Explanation:

  1. The variable isTrue is initialized to true.
  2. Both !isTrue and not isTrue negate the value of isTrue, returning false (0).
  3. The output confirms that not is functionally equivalent to the ! operator.

Example 2: Using not in Conditional Statements

The not keyword can be used in conditional statements to improve code readability.

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#include <iostream>
using namespace std;

int main() {
    bool isAuthenticated = false;

    if (not isAuthenticated) {
        cout << "Access denied. Please log in." << endl;
    } else {
        cout << "Welcome!" << endl;
    }

    return 0;
}

Output:

Access denied. Please log in.

Explanation:

  1. The not keyword is used to check if the value of isAuthenticated is false.
  2. Since isAuthenticated is false, the if condition evaluates to true, and the corresponding block executes.
  3. The output displays an appropriate message for unauthenticated users.

Example 3: Using not with Logical Operators

The not keyword can be combined with logical operators for complex conditions.

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#include <iostream>
using namespace std;

int main() {
    bool isOnline = true;
    bool isInMaintenance = false;

    if (isOnline and not isInMaintenance) {
        cout << "The service is available." << endl;
    } else {
        cout << "The service is not available." << endl;
    }

    return 0;
}

Output:

The service is available.

Explanation:

  1. The condition isOnline and not isInMaintenance evaluates to true because isOnline is true and isInMaintenance is false.
  2. The corresponding if block executes, indicating that the service is available.
  3. The use of not improves readability by clearly expressing the negation.

Key Points to Remember about not Keyword

  • not is an alternative representation of the logical NOT operator (!).
  • It inverts the truth value of a Boolean expression.
  • It can be used interchangeably with !, depending on coding style and readability preferences.
  • It is part of the alternative tokens introduced in C++ to enhance code clarity.
  • Using not can make complex logical expressions easier to understand.