Functions

A C++ program is built out of "functions" — named, reusable blocks of code that perform a specific task. Instead of writing the same instructions over and over, you can define a function once and then "call" it wherever you need that task done.

int addNumbers(int a, int b) {
    return a + b;
}

Every function has a few key parts: a return type (what kind of value it hands back, such as "int" for a whole number, or "void" for nothing at all), a name, a list of parameters in parentheses (the inputs it accepts), and a body in curly braces { } containing the statements it runs.

What is a function in C++?

A function that does not return any value uses the return type "void". For example, a function whose entire job is to print something to the screen usually returns "void", since it doesn't need to hand any value back to whoever called it.

void greet() {
    std::cout << "Hello there!";
}

A function that does not return any value uses the return type ____.

A function can be reused by calling it multiple times, instead of rewriting its code each time.

Every C++ program is a collection of one or more functions. But there is exactly one function that every single C++ program must have — the one where the program actually begins running. That function is called main(), and it's the subject of the next lesson.