A **boolean** data type in C++ is defined using the keyword `bool`. Usually, $1$ (`true`) and $2$ (`false`) are assigned to boolean variables as their default numerical values. Although any numerical value can be assigned to a boolean variable in C++, all values other than $0$ are considered to be `true` and stored as $1$, while $0$ is considered to be `false`. Printing a `bool` variable on a console displays its numerical value.

# Code

#include <iostream>
using namespace std;

int main() {
  // true = 1:
  bool p = true;
  if(p == 1)
    cout << "'p' is true." << endl;
  
  // false = 0:
  bool q = false;
  if(q == 0)
    cout << "'q' is false." << endl;
  
  // Every value other than 0 is stored as 1:
  bool r = -5;
  if(r == 1 && r == true)
    cout << "-5 is stored as 1 in 'r' and it is true." << endl;

  // 0 is stored as it is:
  bool t = 0;
  if(!t)
    cout << "'t' is false." << endl;

  return 0;
}

## Using boolean in a numerical expression

A boolean variable in C++ can be used in a numerical expression as well. As mentioned above, if a `bool` variable is equal to `true`( or any numeric value other than $0$), $1$ is assigned to it and taken as $1$ during the evaluation of the expression; $0$ and `false` will be taken as $0$.

# Code

#include <iostream>
using namespace std;

int main() {
  bool x = 10;  // x = 1;
  bool y = false;  // y = 0;

  // Using bool in a numeric expression:
  cout << 2 * (x + y) << endl;
  
  return 0;
}

What is boolean in C++?

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Using boolean in a numerical expression

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