Not handling user input correctly

Question

So, this program I am working on is not handling incorrect user input the way I want it to. The user should only be able to enter a 3-digit number for use later in a HotelRoom object constructor. Unfortunately, my instructor doesn't allow the use of string objects in his class (otherwise, I wouldn't have any problems, I think). Also, I am passing the roomNumBuffer to the constructor to create a const char pointer. I am currently using the iostream, iomanip, string.h, and limits preprocessor directives. The problem occurs after trying to enter too many chars for the roomNumBuffer. The following screenshot shows what happens:

The relevant code for this problem follows:

cout << endl << "Please enter the 3-digit room number: ";
do {        //loop to check user input
    badInput = false;
    cin.width(4);
    cin >> roomNumBuffer;
    for(int x = 0; x < 3; x++) {
        if(!isdigit(roomNumBuffer[x])) {        //check all chars entered are digits
            badInput = true;
        }
    }
    if(badInput) {
        cout << endl << "You did not enter a valid room number. Please try again: ";
    }
    cin.get();      //Trying to dum- any extra chars the user might enter
} while(badInput);

for(;;) {   //Infinite loop broken when correct input obtained
    cin.get();      //Same as above
    cout << "Please enter the room capacity: ";
    if(cin >> roomCap) {
        break;
    } else {
        cout << "Please enter a valid integer" << endl;
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }
}
for(;;) {   //Infinite loop broken when correct input obtained
    cout << "Please enter the nightly room rate: ";
    if(cin >> roomRt) {
        break;
    } else {
        cout << "Please enter a valid rate" << endl;
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }
}

Any ideas would be greatly appreciated. Thanks in advance.

Answer 1

Read an integer and test whether it's in the desired range:

int n;

if (!(std::cin >> n && n >= 100 && n < 1000))
{
    /* input error! */
}

Answer 2

Although Kerrek SB provide an approach how to address the problem, just to explain what when wrong with your approach: the integer array could successfully be read. The stream was in good state but you didn't reach a space. That is, to use your approach, you'd need to also test that the character following the last digit, ie, the next character in the stream, is a whitespace of some sort:

if (std::isspace(std::cin.peek())) {
     // deal with funny input
}

It seems the error recovery for the first value isn't quite right, though. You probably also want to ignore() all characters until the end of the line.