WinAPI example window

main.c

#include <windows.h>

#define TITLE L"Example Window Title"
#define WIDTH 800
#define HEIGHT 600

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR pCmdLine, int nCmdShow) {
    
    MSG  msg;    
    HWND hwnd;
    WNDCLASSW wc;

    wc.style         = CS_HREDRAW | CS_VREDRAW;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.lpszClassName = L"Window";
    wc.hInstance     = hInstance;
    wc.hbrBackground = GetSysColorBrush(COLOR_3DFACE);
    wc.lpszMenuName  = NULL;
    wc.lpfnWndProc   = WndProc;
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
  
    RegisterClassW(&wc);
    CreateWindowW(wc.lpszClassName, TITLE,
                  WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                  100, 100, WIDTH, HEIGHT, 0, 0, hInstance, 0);  

    while (GetMessage(&msg, NULL, 0, 0)) {
  
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int) msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg,
    WPARAM wParam, LPARAM lParam) {
    
    switch(msg) {
  
        case WM_CREATE: 
      
            CenterWindow(hwnd);
            break;      

        case WM_DESTROY: 
      
            PostQuitMessage(0);
            break;
    }

    return DefWindowProcW(hwnd, msg, wParam, lParam);
}

void CenterWindow(HWND hwnd) {

    RECT rc = {0};
    
    GetWindowRect(hwnd, &rc);
    int win_w = rc.right - rc.left;
    int win_h = rc.bottom - rc.top;

    int screen_w = GetSystemMetrics(SM_CXSCREEN);
    int screen_h = GetSystemMetrics(SM_CYSCREEN);
    
    SetWindowPos(hwnd, HWND_TOP, (screen_w - win_w)/2, 
        (screen_h - win_h)/2, 0, 0, SWP_NOSIZE);
}