Problem when compiling in c++ : "undefined reference to 'WinMain'. Coding a game for mastermind

Question

I'm currently working on an entry level C++ project to code the game mastermind (a secret code is generated and the user tries to crack it). We are just learning the basics of C++ (OOP, arrays and vectors, etc.), so the code seems to work fine. However, everytime I attempt to compile my .cpp files for the 3 classes I have, each one has some error I have never seen referring to WinMain, right here

18 C:\crossdev\src\mingw-w64-v3-git\mingw-w64-crt\crt\crt0_c.c undefined reference to `WinMain' C:\Users\xxx\OneDrive\Desktop\xxx\collect2.exe [Error] ld returned 1 exit status

This is the universal error message across the 3 .cpp files, the header files and main file compile fine. Any ideas what went wrong? I've done a couple assignments similar to this no problem...

Heres the code to one of the classes for reference

#include "response.hpp"

using namespace std;

response::response()
{
    numCorrect = 0;
    numIncorrect = 0;
}


response::response(int correct, int incorrect)
{
    numCorrect = correct;
    numIncorrect = incorrect;
} 


int response::getNumCorrect()
{
    return numCorrect;
} 

int response::getNumIncorrect()
{
    return numIncorrect;
} 


void response::setCorrect(int correct)
{
    numCorrect = correct;
} 

void response::setIncorrect(int incorrect)
{
    numIncorrect = incorrect;
} 

bool operator == (const response& lhs, const response& rhs)
{
    return ((lhs.numCorrect == rhs.numCorrect) && (lhs.numIncorrect == rhs.numIncorrect));
} 

ostream& operator << (ostream& ostr, const response& out)
{
    ostr << "Correct: " << out.numCorrect << endl;
    ostr << "Incorrect: " << out.numIncorrect << endl;
    return ostr;
}