Very often, in programming, you will need a data type that can only have one of two values, like:
- YES / NO
- ON / OFF
- TRUE / FALSE
For this, C++ has a bool data type, which can take the values true (1) or false (0).
Boolean Values
A boolean variable is declared with the bool keyword and can take the values true or false :
Example
bool isCodingFun = true;
bool isFishTasty = false;
cout << isCodingFun << "\n"; // Outputs 1 (true)
cout << isFishTasty << "\n"; // Outputs 0 (false)From the example above, you can read that a true value returns 1 , and false returns 0 .
Printing true/false With boolalpha
If you prefer to print true and false as words instead of 1 and 0 , you can use the boolalpha manipulator:
Example
bool isCodingFun = true;
bool isFishTasty = false;
cout << boolalpha; // enable printing "true"/"false"
cout << isCodingFun << "\n"; // Outputs true
cout << isFishTasty << "\n"; // Outputs falseNote
boolalpha is not a data type. It is an I/O manipulator - a setting that changes how cout displays boolean values. When you use it, you are telling cout : "From now on, print booleans as true and false instead of 1 and 0 ."
Resetting Back With noboolalpha
If you want to go back to the default behavior (printing 1 and 0 ), you can use noboolalpha :
Example
bool isCodingFun = true;
cout << boolalpha; // print as true/false
cout << isCodingFun << "\n"; // Outputs true
cout << noboolalpha; // reset to 1/0
cout << isCodingFun << "\n"; // Outputs 1Note
It is up to you whether you prefer the default 1 and 0 , or the words true and false . Both are correct in C++, and you can switch between them using boolalpha and noboolalpha .
Tip
You can read more about cout and its manipulators in our C++ cout object reference .
In the examples above we used fixed boolean values. But in real programs, boolean values are usually the result of comparing values or variables, which you will learn more about in the next chapter .