C++ Booleans

The Boolean Type

A boolean variable can only be true (1) or false (0). Declare with the bool keyword.

#include <iostream>
using namespace std;

int main() {
    bool isRaining = true;
    bool isSunny   = false;

    cout << isRaining << endl;  // 1
    cout << isSunny   << endl;  // 0
    return 0;
}

Output:

1
0

Printing true / false

By default C++ prints 1 or 0. Use boolalpha to print the words:

cout << boolalpha;
cout << true  << endl;   // true
cout << false << endl;   // false

Boolean Expressions

Any comparison expression evaluates to a boolean:

int x = 10;
cout << boolalpha;
cout << (x > 5)   << endl;   // true
cout << (x == 10) << endl;   // true
cout << (x < 3)   << endl;   // false
cout << (x != 10) << endl;   // false

// Boolean in conditions
bool hasPermission = true;
bool isLoggedIn    = true;

if (hasPermission && isLoggedIn) {
    cout << "Access granted." << endl;
} else {
    cout << "Access denied." << endl;
}

Output:

Access granted.

#include <iostream>
using namespace std;

int main() {
    int age = 20;
    bool isAdult = (age >= 18);
    bool hasID   = true;
    bool canEnter = isAdult && hasID;
    cout << boolalpha;
    cout << "Can enter: " << canEnter << endl;
    return 0;
}

Summary

• bool stores only true (1) or false (0).
• Use boolalpha to print the words "true" / "false".
• Comparison and logical expressions evaluate to booleans.