Question

Consider the following code:

float validateEntry()
{
    string entry;
    float value;

    getline(cin, entry);
    value = atof(entry.data());

    return ((isNumber(entry) && value >= 0) ? i
    : (cout << "Enter valid amount: ", validateEntry())
}

Why is the last line (the comma-separated expression) allowed, and are there other expressions that can be used with return statements in C++?

I’m mostly confused at the use of the comma, and wondering where this expression syntax is defined (I had no idea it existed, nor would I have known where to find out). Can I fill that last expression with an indefinite amount of code; if so, what are the limitations, requirements, etc.?

Answer 1

The comma operator allows you to group two otherwise-unrelated expressions. Both expressions are always evaluated, and the result is the result of the second expression. It is almost always a bad idea to use it (because it hurts readability just to save a line of code), except maybe in the top of a for-loop.