#include <iostream>                // Ex18
using namespace std;
int main() {
    int n;
    for ( ;; ) {
        cout << "Enter a number: ";
        cin >> n;
      if ( cin.eof() ) break;    // eof ?
        if ( ! cin.fail() ) {    // number ?
            cout << "n = " << n << endl;
        } else {
            cout << "Not a number. ";
            cin.clear();        // reset stream failure
            cin.ignore( numeric_limits<int>::max(), '\n' );  // skip until newline
        }
    }
    cout << endl;
}