5.9. Returning from main¶

Now that we have functions that return values, I can let you in on a secret. main is not really supposed to be a void function. It’s supposed to return an integer:

int main () {
  return 0;
}

The usual return value from main is 0, which indicates that the program succeeded at whatever it was supposed to do. If something goes wrong, it is common to return -1, or some other value that indicates what kind of error occurred.

Of course, you might wonder who this value gets returned to, since we never call main ourselves. It turns out that when the system executes a program, it starts by calling main in pretty much the same way it calls all the other functions.

There are even some parameters that are passed to main by the system, but we are not going to deal with them for a little while.

Q-1: What data type is the main function supposed to return?

string
Look at the function definition for main.
integer
Correct! You should always return an integer to avoid issues down the road.
nothing
Main is supposed to return something!
anything
Main has a return type, check its function definition.

Q-3: What gets printed when the following code runs?

int main() {
    bool sun_set=true;
    if(sun_set) {
        cout << "its night time ";
        sun_set=false;
        return 0;
    }
    if(!sun_set) {
        cout << "Day time ";
    }
    else {
        cout << "afternoon ";
    }
}

"its night time Day time"
a return statement if encountered before reaching the second ``if``.
"its night time afternoon"
a return statement is encountered before and ``sun_set`` is false.
nothing is printed
``sun_set`` is true so the "its night time" gets printed
"its night time"
Correct! Once the ``return`` statement is encountered nothing else is printed