Fourier Analysis Rectangle Signal

#define _USE_MATH_DEFINES

#include <iostream>
#include <cmath>
#include <fstream>

int main()
{
    const double begin = 0.0;
    const double end = 2 * M_PI;
    const double step = 0.0001;
    double c_step = begin;
    double temp = 0.0;

    const int n = 15000;        //Number of summed signals

    std::ofstream file;
    file.open("Fourier.csv");

    file << "t" << ";" << "f(x)" << std::endl;

    while (c_step <= end) {

        for (int i = 1; i <= n; i++) {
            temp = temp + 0.5 * (sin((2 * i - 1) * end * c_step)) / (2 * i - 1);
        }

        std::cout << "Progress: " << (c_step / end) * 100 << "%" << std::endl;

        file << c_step << ";" << temp << std::endl;
        c_step += step;
        temp = 0.0;
    }

    file.close();

}