Boolean values | C++ Quick Reference

At a glance

Value or operation	Result
`false`	Converts to and prints as `0`
`true`	Converts to and prints as `1`
Integer `0` converted to `bool`	`false`
Any nonzero integer converted to `bool`	`true`
`!value`	Flips `true` and `false`
`bool value {};`	Initializes `value` to `false`

bool isReady { true };
isReady = !isReady; // false

Printing and input

By default, std::cout prints Booleans as 1 and 0. Use std::boolalpha to print the words true and false:

std::cout << std::boolalpha;
std::cout << true;  // true
std::cout << false; // false

std::cout << std::noboolalpha;
std::cout << true;  // 1

By default, std::cin expects 0 or 1. Enable std::boolalpha on the input stream to read the lowercase words true and false:

bool value {};
std::cin >> std::boolalpha >> value;

Input and output formatting are controlled separately: configure std::cin and std::cout individually. Use std::noboolalpha to switch either stream back.

Common use

Comparisons produce Boolean values, so a checking function can return the comparison directly:

bool isEqual(int x, int y)
{
	return x == y;
}

Functions that answer a yes-or-no question are commonly named with is or has, such as isEqual() or hasCommonDivisor().