#include <iostream>
#include <fstream>
#include <string>

using namespace std;

void main()
{
	//Open "input.txt" for reading.
	fstream fin("input.txt");

	//Open "output.txt" for writing - the ios::out parameter is required. This will overwrite if applicable.
	fstream fout("output.txt", ios::out);

	//Make sure "input.txt" and "output.txt" were opened properly.
	if (fin && fout)
	{
		//Tell them we're adding commas.
		cout << "Adding commas...\n\n";

		//This will hold each line of characters that we read and write.
		string nextLine = "";

		//This is an infinite loop - it will only break (exit) from the loop when we've reached the end of the file.
		while (true)
		{
			//Read the next line from the file.
			getline(fin, nextLine);
			
			//Check to see if we've reached the end of the file. If so, break out of the reading/writing while loop.
			if (!fin)
			{
				break;
			}

			if (nextLine.length() > 2)
			{
				nextLine.insert(3, ",");
			}

			//Output the next line.
			fout << nextLine << '\n';
		}

		//Assume success since there were no file opening errors.
		cout << "Adding commas successful! Check \"output.txt\".";
	}
	else
	{
		//The files were not opened properly - let the user know that it was unsuccessful.
		cout << "Error either opening \"input.txt\" for reading or opening \"output.txt\" for writing.";
	}

	//Close the files.
	fout.close();
	fin.close();

	//Output some new line characters before the program asks for a key press.
	cout << "\n\n";

	system("pause");
}