guys, im trying to separate certain functions into another file with headers, but i ran into problem with undefined reference to `make_histogram(std::vector<double, std::allocator > const&, unsigned long&). histogram.h and histogram.cpp is located in one folder without any subfolders.

main.cpp

#include <vector>
#include <iostream>
#include "histogram.h"
using namespace std;

struct Input {
    vector<double> numbers;
    size_t bin_count{};
};

Input
input_data() {
    Input in;

    size_t number_count;
    cerr << "Enter quantity of numbers: ";
    cin >> number_count;

    vector<double> numbers(number_count);
    in.numbers.resize(number_count);
    cerr << "Enter numbers: ";
    for (size_t i = 0; i < number_count; i++) {
        cin >> in.numbers[i];
    }

    cerr << "Enter bin count: ";
    cin >> in.bin_count;

    return in;
}

int
main(){
    auto in = input_data();
    auto bins = make_histogram(in.numbers, in.bin_count);
    show_histogram_text(bins, in.bin_count);
}

histogram.h

#ifndef HISTOGRAM_H_INCLUDED
#define HISTOGRAM_H_INCLUDED

#include <vector>
#include <iostream>
using namespace std;

vector<size_t>
make_histogram(const vector<double>& numbers, size_t & bin_count);

void
find_minmax(const vector<double>& numbers, double& min, double& max);

void
show_histogram_text(vector<size_t>& bins, size_t& bin_count);

#endif // HISTOGRAM_H_INCLUDED

histogram.cpp

#include "histogram.h"

vector <size_t>
make_histogram(const vector<double>& numbers, size_t & bin_count) {
    double min, max;
    find_minmax(numbers, min, max);
    double bin_size = (max - min) / bin_count;
    vector<size_t> bins(bin_count);
    size_t max_count = bins[0];
    for (size_t i = 0; i < numbers.size(); i++){
        bool found = false;
        for (size_t j = 0; (j < bin_count - 1) && !found; j++){
            auto lo = min + j * bin_size;
            auto hi = min + (j + 1) * bin_size;
            if ((lo <= numbers[i]) && (numbers[i] < hi)){
                bins[j]++;
                found = true;
            }
            if (bins[j] > max_count){
                max_count = bins[j];
            }
        }
        if (!found){
            bins[bin_count - 1]++;
        }
        if (bins[bin_count - 1] > max_count){
            max_count = bins[bin_count - 1];
        }
    }
    return bins;
}

void
find_minmax(const vector<double>& numbers, double& min, double& max) {
    if (!numbers.empty()) {
        min = numbers[0];
        max = numbers[0];
    } else {
        min = 0;
        max = 0;
    }
    for (double x : numbers)
    {
        if (x < min){
            min = x;
        }
        else if (x > max){
            max = x;
        }
    }
}

void show_histogram_text(const vector<size_t>& bins, size_t& bin_count) {
    const size_t SCREEN_WIDTH = 80;
    const size_t MAX_ASTERISK = SCREEN_WIDTH - 3 - 1;

    int max_count = 0;
    for (int i =0; i<bin_count;i++){
        if (bins[i]>max_count){
            max_count=bins[i];
        }
    }
    if (max_count>MAX_ASTERISK){
        for (int i=0; i<bin_count; i++){
            size_t height = MAX_ASTERISK * (static_cast<double>(bins[i]) / max_count);
            if (bins[i]<10){
                cout<<"  "<<bins[i]<<"|";
                for (int j=0;j<height;j++){
                    cout<<"*";
                }
                cout<<endl;
            }
            else if(bins[i]<100){
                cout<<" "<<bins[i]<<"|";
                for (int j=0;j<height;j++){
                    cout<<"*";
                }
                cout<<endl;
            }
            else{
                cout<<bins[i]<<"|";
                for (int j=0;j<height;j++){
                    cout<<"*";
                }
                cout<<endl;
            }

    }
    }else{
        for (int i=0; i<bin_count; i++){
            if (bins[i]<10){
                cout<<"  "<<bins[i]<<"|";
                for (int j=0;j<bins[i];j++){
                    cout<<"*";
                }
                cout<<endl;
            }
            else if(bins[i]<100){
                cout<<" "<<bins[i]<<"|";
                for (int j=0;j<bins[i];j++){
                    cout<<"*";
                }
            cout<<endl;
            }
            else{
                cout<<bins[i]<<"|";
                for (int j=0;j<bins[i];j++){
                    cout<<"*";
                }
                cout<<endl;
            }

        }
    }
}

Where could the problem be? Help, please <3