#include <iostream>
using namespace std;

// add pairs of numbers

// description of cin functions @ http://www.cplusplus.com/ref/iostream/istream/


// read integer from cin, repeat if error

int read_int()
{
  int number;
  
  do {

    cin >> number;
    if (cin.good()) break; // input OK -> exit loop

    cout << "input error! try again" << endl;      
      
    cin.clear();           // clears stream error flags

    char c;                // skips input until '\n' is read
    do {
      c = cin.get();
      if (!cin.good()) { cerr << "read error" << endl; exit(10); }
    } while (c != '\n');
    
  } while (true);

  return number;
}


int main() {

  int number1, number2;
  
  do {

    // read first number
    cout << "number 1 = " << flush;
    number1 = read_int();

    // read second number
    cout << "number 2 = " << flush;
    number2 = read_int();

    // print result
    cout << "sum = " << number1 + number2 << endl << endl;
    
  } while (true);            // loop forever

}