How to read multiple input files and write into a new file in txt and excel in C++?

I used to run a calculation by reading from 1 txt file ("1_Hello.txt"), calculate and output by functions, and write the output into a new txt file.

But now I have 5000 txt files ("1_Hello.txt" to "5000_Hello.txt"). I want to read all 5000 txt files, calculate each txt file by functions ( variable "a" and vector "v"), and write the output of these 5000 files into a new txt file and a new excel file that contains calculated results of all 5000 input files.

Input format: id x y z

Ex: 1 9 7 5

Wanted output format: id x y z add() int_vector()

Ex: 1 9 7 5 5.5 123

How can I read 5000 txt files and write the calculated results from functions into new txt and excel files?

Any help would be appreciated.

      double add(){
      // do something
      }

      void output_vector(std::vector<int> &v) {
      // do something
      }

        int main() {
        std::vector<int> v;
        double a;

        ifstream in("1_Hello.txt");
        in.close();

        a=add();
        output_vector(v);

        return 0;
     }

Solution

Here is some very simple and incomplete code that might help along the way:

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

int main(int argc, char* argv[]) {
    /* define some vectors to store the data in */
    std::vector<int> id_vec;
    std::vector<int> x_vec;
    std::vector<int> y_vec;
    std::vector<int> z_vec;
    std::vector<double> calc_1_vec;
    std::vector<double> calc_2_vec;
    
    for (int i = 1; i < 5001; ++i) {
        std::string file_name = std::to_string(i) + std::string("_hello.txt");
        std::ifstream input_file (file_name);
        if (input_file.is_open()) {
            /* read whatever is in the file, maybe in a loop if there is more stuff in it */
            /* then close it */
            input_file.close();
            /* parse the input line and store the values in some variables */
            /* calculate whatever it is that you need to calculate */
            /* then store the calculated values in the vectors */
            /* also store the read values in the vectors */
        }
        else {
            std::cout << "could not open file" << std::endl;
        }
    }
    /* sort the vectors according to your needs */
    /* make sure that zou change the other vectors accordingly */
    /* so if you switch the 3. and the 4. index in the ID vector */
    /* then also switch those in the other vectors */
    
    /* open up the output file and write the vectors into the files */
}

And of course there are better solutions, like using std::filesystem to read all files in a directory that match a certain pattern.

Another improvement would be to only have one vector and define a struct that you store in that vector. This struct then has the ID, X, Y, Z and calculated fields. Then you could use some sort function from the standard library. The you could have member functions that handle the calculations, printing, etc.

struct data {
    int id;
    int x;
    int y;
    int z;
    double calc_1;
    double calc_2;
};

Then later simply:

std::vector<data> data_vec;