#include <iostream>
using namespace std;

// function prototypes
void clrStream();         // clear to end of line
char getResponse(char defalt);
void getValid(int& i);    // obtain a valid int from the user

int main()
{
   char answer;
   do {
      int sum = 0;
      int value;
      do {
	 getValid(value);
	 if (cin) sum += value;
      } while (!cin.eof());
      cout << "The sum is " << sum << endl;
      cout << "Would you like to do another sum (No to stop)? ";
      cin.clear();   // reset eof flag
   } while (getResponse('Y') != 'N');  
   return 0;
}

//**************************************************************************
// function to clear the data from the cin stream up to and including the
// next new line character.
//**************************************************************************
void clrStream() {
   while (cin.peek() != '\n') cin.ignore();
   cin.ignore();    // ignore the newline as well
}

//**************************************************************************
// function to get a character response from the user and use the default
// response if the user just hits the return key
//
/// \param [in] defalt imports the default character to use if the enter
///                    key is pressed
/// \returns defalt if the next character in the cin stream is a new line,
///                  otherwise it returns the character entered
/// \post the cin stream is cleared
//**************************************************************************
char getResponse(char defalt) {
   char ch = cin.get();
   if (ch == '\n')
      ch = defalt;    // use the default character
   else
      clrStream();    // clear the newline and any garbage entered

   return ch;
}

//**************************************************************************
// function to get a valid int
//
// parameter usage -- i exports the integer obtained
//
// post-condition -- i is a valid integer and the cin stream marker is left
//                   at the first character after the extracted integer
//**************************************************************************
void getValid(int& i) {
   while (!(cin>>i || cin.eof())) {  
      cout << "Invalid integer entered!! Reenter -- ";
      cin.clear();   // clear the error flag
      clrStream();   // clear bad data from the stream
   }
}  

//  while (!(cin>>i) && !cin.eof()) {  // alternate version of while loop