C++ Booleans

A boolean variable is declared with the keyword bool and can hold only one of two values: true or false. These are actual keywords in C++, so you write them in lowercase and without quotes.

#include <iostream>
using namespace std;

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

  cout << isCodingFun << "\n"; // 1
  cout << isRaining << "\n";   // 0
  return 0;
}

Booleans from comparisons

Most of the time you will not type true or false yourself. Instead, a boolean is produced when you compare two values using comparison operators such as > (greater than), < (less than), and == (equal to). The comparison evaluates to either true or false.

#include <iostream>
using namespace std;

int main() {
  int x = 10;
  int y = 9;

  cout << (x > y) << "\n";  // 1 (true, 10 is greater than 9)
  cout << (x == y) << "\n"; // 0 (false, they are not equal)

  bool result = 5 > 3;
  cout << result << "\n";   // 1 (true)
  return 0;
}

Common comparison operators

Why booleans matter

• They control if statements, deciding which branch of code runs.
• They keep loops going or stop them.
• They can store the answer to a yes or no question, like whether a user is logged in.
• They combine with logical operators (&&, ||, !) to express complex conditions.