blank win32 application

#include <Windows.h>
#include <iostream>
#include <string>
#include <string.h>

// Global Variables
HINSTANCE hInstance;         //the current instance
const char* WindowTitle;     //The title of the window
const char* WindowClassName; //the class name

LRESULT    CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM); //Used for getting messages and stuff from e.g, moving your mouse
WNDCLASS               RegisterWindowClass(HINSTANCE); //registers the class in windows so you can show it
BOOL                   InitInstance(HINSTANCE, int);  //initialises the class and window

void                   InitVariables(); //used to declare the window title, class name, etc.

#define DefaultWindowStyle (WS_POPUP | WS_HSCROLL | WS_SYSMENU | WS_CAPTION| WS_SYSMENU | WS_THICKFRAME | WS_MINIMIZEBOX |WS_TABSTOP| WS_MAXIMIZEBOX)

int WINAPI WinMain(HINSTANCE currentInstance, HINSTANCE prevInstance /*this is always null*/, PSTR cmdLineArgs, INT cmdShow)
{
    InitVariables();

    //the & fetches the address of the RegisterWindowClass "variable" so it can be pointed to. cpp magic basically
    RegisterClass(&RegisterWindowClass(currentInstance));

    if (!InitInstance(hInstance, cmdShow))
        return FALSE;

    MSG msg{};
    //this will be running forever until the window is closed. GetMessage constantly loops getting system messages like mouse moves, etc
    while (GetMessageA(&msg, nullptr, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessageA(&msg);
    }

    return 0;
}

//Setting up the variable init thing
void InitVariables()
{
    WindowTitle     = "A title here";
    WindowClassName = "A class name here";
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
    case WM_DESTROY: //clicking the X button on the window basically
        PostQuitMessage(0); //tells the program to exit
        break;
    default:
        return DefWindowProcA(hWnd, msg, wParam, lParam);
        break;
    }
}

WNDCLASS RegisterWindowClass(HINSTANCE instance)
{
    WNDCLASS wc{};
    wc.hInstance = instance;
    wc.lpszClassName = WindowClassName;
    wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    wc.lpfnWndProc = WndProc;
    return wc;
}

BOOL InitInstance(HINSTANCE instance, int cmdShow)
{
    hInstance = instance; //stores the global instance as this method's instance

    HWND hWnd =
        CreateWindowA(
            WindowClassName, WindowTitle,     //Gives it the class and title
            DefaultWindowStyle,               //Window style
            CW_USEDEFAULT, CW_USEDEFAULT,     //initial window position
            900 /*width*/, 450/*height*/,
            nullptr, nullptr, hInstance, nullptr
        );

    if (!hWnd)
        return FALSE; //same as 0

    ShowWindow(hWnd, cmdShow); //actually shows the window on your screen
    UpdateWindow(hWnd);
    return TRUE; //lets other code know it's shown correctly
}