while ((std::cout << "Enter a number: ") && !(std::cin >> integer))
{
    std::cout << "OK, that's not a number, genius." << std::endl;
    std::cin.clear();
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

#include <iostream>

using namespace std;

int getStrength ()
{
    unsigned int strength;
    unsigned int tries = 0;

    cout << endl << "Enter strength: ";
    while (true)
    {
        if (tries > 3)
        {
            cout << "You just can't get it, can you?" << endl;
            return -1;
        }
        // The following clears the error bits for the stream,
        // in case some usage broke it.
        cin.clear ();
        // Adjust the stream related pointers.  For istreams,
        // this effectively clears content.  It's possible for
        // it to fail.  Some istreams might not have buffers;
        if (cin.sync () == -1) return -1;
        cin >> strength;
        if (!cin.good ()) cout << "Invalid input; try again: ";
        else if (strength > 20) cout << "Invalid number, try again: ";
        else return strength;
        tries++;
    }
    return -1;
}