Function to read an integer OR a float from a std::istream.

readIntOrNotFloat.cpp

///@return true if int, false if float
bool readIntOrNotFloat( std::istream& in, int& i, float& f ) {
  in >> i;
	if( in.good() ) {
		char c = in.peek();
		if( c == '.' ) {
			in >> f;
			f += i;
			return false;
		}
	}
	return true;
}

test.cpp

  
int i = 0;
float f = 0;

bool bool int_or_notFloat = 42; //Always a good thing to init a varaible...
cout << "Enter an integer or a float (anything else to exit)\n";
while(cin) {
    cout << "? ";
    int_or_notFloat = readIntOrNotFloat(cin, i, f);
    if(cin) {
      if( int_or_notFloat ) {
          cout << "Got an integer: " << i << endl;
      } else {
          cout << "Got a float: " << f << endl;
      }
    }
}