Question

Usually I write a control loop as follows:
Loop that enters writes ints into vector nVec until “done” is entered.

while (cin >> sString){
    if (sString="done")
    { 
        break;
    }
    nVec.push_back(sString);

}

this works fine, but how would I go about doing this if I wanted the loop to end once the user entered nothing (just pressed enter)?

Answer 1

You can’t “not enter anything” into your token-wise extraction. The only way for your loop to stop is for the user to send end-of-file (Ctrl-D on Linux). I would personally say that this is the correct behaviour, but if you want to end on empty input, you need to read lines:

Sales_item total;

for (std::string line; std::getline(std::cin, line); )
{
     if (line.empty()) { exit_program(); /* or "break" */ }

     std::istringstream iss(line);
     for (Sales_item book; iss >> book; )
     {
          total += book;
          std::cout << "The current total is " << total << std::endl;
     }
}

This way, you tokenize each line into possibly multiple books. If you just want one book per line, rip out the inner loop and just say std::istringstream(line) >> book;.