Welcome to Programming and Data Structures

After all those details, it is worth briefly reviewing when you should throw an exception. To do this, it helps to imagine that every function is written by a different programmer. Those programmers working on higher level functions know something about lower level ones, but not all of the details. The programmers of low level functions might know nothing at all about higher level ones.

In this situation, stringToBool will be the place that the code recognizes stringToBool("cat") is a problem. But the code that knows what to do about that problem is higher up. So stringToBool should throw an exception and let a higher level function deal with it.

Using exceptions, here is what our stringToBool could look like:

bool stringToBool(const string& s) {
    if (s == "true") {
        return true;
    } else if (s == "false") {
        return false;
    }
    string errorMessage = "Invalid string for boolean conversion: " + s;
    throw logic_error(errorMessage);
    return false; // We will never reach this line
}

When the function can’t do its job, it makes a message on line 7 and then throws that message on line 8. Line 9 will never execute because of the throw. But some compilers will still want to see that the function ends with a return. In cases like that, it is typical to return some default value and leave a comment to note that the line is just there to make the compiler happy.