Error LNK2005: function already defined in MyForm.obj - c++

Question

I'm trying to make a windows form application in Visual Studio C++, but I get this errors after compiling, for each function:
error LNK2005: function already defined in MyForm.obj
These are my files:
Source.cpp
#pragma once
#include "MyForm.h"
using namespace System;
using namespace System::Windows::Forms;
[STAThread]//leave this as is
void main() {
Application::EnableVisualStyles();
Application::SetCompatibleTextRenderingDefault(false);
Application::Run(gcnew Project1::MyForm);
}
MyForm.h
#pragma once
#include <iostream>
#include <string>
#include "Header.h"
namespace Project1 {
//codes of te form
}
Header.h
#pragma once
#include <iostream>
#include <string>
#include <cmath>
#include <set>
#include <algorithm>
using namespace std;
int n, m;
int size1, size2;
//My functions here
So how can I fix errors?

Answer 1

If you declare and implement a function in a header file (Header.h) and if this file gets included twice, then you'll most likely will get a function already defined error at some point.
This can be fixed by either:
Moving function implementation to a source (cpp) file and only keep it's declaration in the header (h) file
Make the function inline (if it is acceptable), that will remove the error