Help with outputting a list of squared numbers

[dnguyen1022]

So my program is suppose to take in a single number and output all numbers starting from 0 up to that given number squared. I believe this is quite an easy problem but I am struggling with it when it includes headers and source files. I am getting an 'undefined reference to 'squaredint...'' error. I do not understand why it is getting this error though, but I do see where it occurs.
Here is the coding for my main, source, and header files.

main

#include "squaredintheader.h"
#include <conio.h>
#include <iostream>

using std::cout;
using std::endl;
using std::cin;

int main(){
    
    int num;
    
    cout << "Up to what number do you want squared? " << endl;
    cin >> num;
    
    //the whole squared numbers
    number_info numbers = squaredint(num, numbers);
    
    //outputs the number with the squared numbers
    for(int i = 0; i != numbers.number.size(); i++){
            cout << i << " " << numbers.squared[i] << endl;
            }
            
    cout << "Press enter to continue..";
    _getch();
    return 0;
    }

header

#ifndef GUARD_squarednum_h
#define GUARD_squarednum_h

#include <vector>

//squaredintheader.h
struct number_info{
       std::vector<int> number;
       std::vector<int> squared;
};

number_info squaredint(const int&, number_info&);

#endif

source

#include "squartedintheader.h"
#include <vector>

using std::vector;

number_info squaredint(const int& upto, number_info& squaredlist){
           
            //adds the given number and squared number
            //to the struct of int vectors
            for(int i = 0; int != upto; i++){
                    squaredlist.number.push_back(i);
                    squaredlist.squared.push_back(i*i);
                    }
            }

Thanks for your help!