#include <fstream>
#include <iostream>
#include <string>
using namespace std;
 
bool validChar (int n)
{
  bool result = false;
  if ((n > 47 && n < 58 ) || (n > 64 && n < 91)|| (n > 96 &&  n < 123)
    || (n == 43) || (n == 45) || (n == 46) ||(n == 95)) result = true;
  return result;
}
 
int main()
{
  string defInFile = "fileContainingEmails.txt";
  string defOutFile ="copyPasteMyEmails.txt";
  string inFile;
  string outFile;
 
  cout << "\n Enter the input file name, leave blank for fileContainingEmails.txt: ";
  getline(cin, inFile);
 
  if (inFile.length()==0)
  {
    inFile=defInFile;
    outFile=defOutFile;
  }
  else outFile=inFile;
 
cout << "inFile is " << inFile << endl;
cout << "outFile is " << outFile << endl << endl;
 
  string temp;
  cout << "\n Enter the output file name, leave blank for " << outFile << ": ";
  getline(cin, temp);
 
  if (temp.length()==0) outFile=outFile;
  else outFile=temp;
 
cout << "\n inFile is " << inFile << endl;
cout << " outFile is " << outFile << endl << endl;
 
 
  ifstream fin;
  ofstream fout;
 
  fin.open(inFile.c_str());
  if (!fin.good()) throw "I/O error";
 
  int s, e;
  string anEmail;
  while (true)
  {
    if (!fin.good()) break;
 
    string line;
    getline(fin, line);
 
    for (int i = 0; i < line.length(); i++)  // as long as i is < entire length of line, increment by 1
    {
      if (line[i]==64) // if @ symbol present, print line
      {
        for (s = i; s > 0; s--)
        {
          if (!validChar(line[i])) break;
        } // for
        s++;
cout << "         S IS    " << s << endl;
 
        for (e = i; e > line.length(); e++)
        {
          if (!validChar(line[i])) break;
          if (line[i] == line.length()) break;
        }  // for
 
        anEmail = line.substr(s, e-s);
cout  << "      anEmail     : " << anEmail << endl;
        }  // if
    }  // for
  }  // while
  fin.close();
  return 0;
}