C++ Booleans

The bool type stores one of exactly two values, true or false, and drives the decisions made by every conditional statement and loop in a C++ program.

In this page:

The bool Type
Boolean Expressions
Booleans in Conditions
Boolean Variables from Comparisons
Printing Booleans with boolalpha

The bool Type

The bool type represents exactly one of two possible values, true or false, and is C++'s dedicated type for logical values, used whenever a piece of information is a simple yes-or-no flag.

Example: The bool Type

cpp

#include <iostream>

int main() {
	bool isSubscribed = true;
	std::cout << isSubscribed << std::endl;
	return 0;
}

Boolean Expressions

A boolean expression is any expression that evaluates to true or false, most commonly formed by comparing two values with operators like >, <, ==, or != rather than by writing a literal true or false directly.

Example: Boolean Expressions

cpp

#include <iostream>

int main() {
	int x = 10;
	bool result = x > 5;
	std::cout << result << std::endl;
	return 0;
}

Booleans in Conditions

Boolean values are what control flow statements like if, while, and for actually test: an if statement runs its block only when the boolean expression inside its parentheses evaluates to true.

Example: Booleans in Conditions

cpp

#include <iostream>

int main() {
	bool isOpen = true;
	if (isOpen) {
		std::cout << "Store is open" << std::endl;
	}
	return 0;
}

Boolean Variables from Comparisons

Storing the result of a comparison in a named bool variable, rather than repeating the comparison inline, makes conditions easier to read and lets the same computed result be reused in multiple places.

Example: Boolean Variables from Comparisons

cpp

#include <iostream>

int main() {
	int score = 70;
	bool passed = score >= 60;
	if (passed) {
		std::cout << "Passed" << std::endl;
	}
	std::cout << passed << std::endl;
	return 0;
}

Printing Booleans with boolalpha

By default cout prints a bool as 1 or 0, but the boolalpha stream manipulator makes it print the words true and false instead, which can be more readable in output.

Example: Printing Booleans with boolalpha

cpp

#include <iostream>

int main() {
	bool active = true;
	std::cout << active << std::endl; // 1
	std::cout << std::boolalpha << active << std::endl; // true
	return 0;
}

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