for(int i = startnum; i <= endnum; i++) {  // Appropriately create filename to open  // By the way, itoa() is awful - non-standard and ancient. I'll redo  // this part using modern tools:  stringstream filenameBuilder("./CampaignID");  // by the way, use forward slashes in your file names, even on platforms  // where that isn't the filename separator - see here:  // http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.16  filenameBuilder << setfill('0') << setw(6) << i << "-OpenedEmail.txt";  // Now we can open the file:  ifstream in(filenameBuilder.str().c_str());  // Yes, those three lines really replace all of your filename construction  // code, and also create a new ifstream object each time through the loop  // with the appropriate filename. :)    // While possible to read a line. If the file couldn't be opened,   // this will fail right away and do nothing, just as it did before.  // This also fixes the bug whereby .eof() doesn't return true until *after  // a failed read*, which would add a duplicate of the last line to your output  // (assuming I'm thinking clearly).    while(in >> date >> time >> meridian >> email) {    out << i << "," << date << " " << time << " " << meridian         << "," << email << endl;  } // 'i2a' previously just held a string representation of the number, and    // outputting a number to a stream with operator<< works just fine, so I    // just substituted the actual number there.}// No cleanup is needed: this ends the scope so the current ifstream will have// its destructor called (closing the file automatically), and a new one is// constructed next time through. None of the strings really need to be// re-initialized because we'll only ever output them when we were successful// in reading values into them (this holds for the original code too).// The i2a buffer didn't need to be cleaned up before, either, but now it// isn't even present. I'd just like to comment that setting individual // *characters* to 'NULL', while it may work, is misleading: C++ defines// NULL as 0, which happens to be the necessary value for null termination,// but it's really meant to indicate a null *pointer*. For chars, use '\0'// instead.