Thread: stream - discard the valid input

Hi all,

i was trying to type the same program from a book that does the following:
Program requests to enter a number 0 -100.
The program checks if the entry is valid, if not, the faildbit should be cleared (cin.clear) and invalid entry discarded (cin.ignore).

if itry this code and enter a text instead of a number, i run into an endledd loop of "Invalid number. Try again"

Code:

    while (true) {
        cout << "Enter a number between 0 - 100" << endl;
        cin >> d;


        if (!cin.good()) {
            cout << "Invalid input. Try again" << endl;
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
            cin.clear();
            continue;
        }
        if (d < 0 || d > 100) {
            cout << "Wrong range. Try again" << endl;
        }
        else {
            cout << "You entered " << d << endl;
            break;
        }
    }
    return 0;

checking the book again, i saw i switched 2 lines. i should ignore than clear

Code:

cin.ignore(numeric_limits<streamsize>::max(), '\n');
cin.clear();

i dont' unterstand how the order of those 2 lines, is having this impact? it seems for me also correct, to discard first and clear the failbits.

i wouls be gratefull for any hints

The order matters. If the stream enters a fail state no further processing of that stream can occur until the errors are cleared. This means that the clear() must be the first thing done.

That makes a lot of sense, thanks a lot, a very useful info