c++ - While loop with try catch fails at bad cin input

Question

I can't seem to figure out why this falls into a loop after getting non-int input. I've tried cin.flush(), which doesn't seem to exist, cin.clear(), which seems like it should work, even cin.sync() after reading someone else post about it working, but didn't seem to make much sense. Also tried cin.bad().

Thank you very much for any help

Please enter the first number: f Sorry, I don't think that's a number?

Please enter the first number: Sorry, I don't think that's a number?

Please enter the first number: Sorry, I don't think that's a number?

Please enter the first number: Sorry, I don't think that's a number?

Please enter the first number: Sorry, I don't think that's a number?Sorry, you d on't get any more tries. Press any key to continue . . .

#include <iostream>
using namespace std;

int main(){
    int entry;
    int attempts = 1;
    int result;
    while(attempts <= 5) {
        try {
            cout << "

Please enter the first number: ";
            cin >> entry;
            if (cin.fail())
                throw "Sorry, I don't think that's a number?";
            if (entry < 0)
                throw "Sorry, no negative numbers. Try something else? ";
            cout << "
Now the second number: ";
            cin >> entry;
            cin.clear();
            cin.get();
        }
        catch (char* error) {
            cout << error;
            attempts++;
        }
    }
    if (attempts > 5)
        cout << "Sorry, you don't get any more tries.
";
    system("pause");
    return 0;
}

Answer 1

You should think carefully what you want to do if user gives invalid input in this case. Usually in these cases the best solution is to read one line from the input and throw it away.

Try putting cin.clear() and std::cin.ignore(std::numeric_limits<streamsize>::max(),' '); in your catch clause. cin.clear() clears the failure state in cin, and cin.ignore() throws away rest of the line waiting in the input buffer.

(And yes, you probably should rethink your use of exceptions).