This is not exactly what you are asking but I am sure this will help you.
Code:
/* Number or alphabetes detection demo code */
#include <iostream>
#include <string>
using namespace std;
int main()
{
 int x = 0;
 string badChars;
 do {
  cout << "Enter a number (-1 = quit): ";
  if(!(cin >> x)) {
   cin.clear();
   cin >> badChars;
   cout << "You typed string \"" << badChars << "\" instead of a number!" << endl;
   cout << "Please try again." << endl;
  } else if(x != -1) {
   cout << "You entered digit!" << x << endl;
  }
 } while(x != -1);
 cin.get();
 return 0;
}