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

using namespace std;

int main()
{
    string GetString;
    for (int i = 1; i <= 5; i++)
    {
        stringstream InputFileName;
        stringstream OutputFileName;
        InputFileName << "C:\\XXX\\" << "data_" << i << ".txt";
        OutputFileName << "D:\\XXX\\" << "newdata_" << i << ".txt";

        ifstream InputFile(InputFileName.str());
        ofstream OutputFile(OutputFileName.str(), ios::app);

        if (!InputFile.is_open())
        {
            cout << "failed to open " << i << endl;
        }
        while (getline(InputFile, GetString))
        {
            OutputFile << GetString;
            OutputFile << endl;
        }
        InputFile.close();
        OutputFile.close();
    }
    while (1);
    return 0;
}