Problem with check box in Win32

Again, this part of code is irrelevant.
—SA

Think in terms of communication. A separate project. And it's good to develop a habit of developing all kinds of prototype and study projects which don't go in the final product but are stored in your revision control database. (If you are not using revision control, you should start immediately.) When you have less experience, you make less such projects, but with time you will have less of them, but they never go, as soon as you do anything serious for you...
—SA

Not at all. Please see my answer. Play with it. I haven't worked with that pretty lame Windows messaging stuff for a long time, but never faced any serious problems; it's all pretty simple.
—SA

Your condition is invalid, check the documentation an rewrite if else properly

First read this manual
https://msdn.microsoft.com/en-us/library/windows/desktop/bb761879%28v=vs.85%29.aspx

go back to your original code and check it this way,

if (checked==BST_CHECKED) {

Changed your `bool checked =` to `int checked`

I will remind you again, please read the manual
https://msdn.microsoft.com/en-us/library/windows/desktop/bb761879%28v=vs.85%29.aspx

This is a source code, made for you just to test if it works

// echeck.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "echeck.h"

#define MAX_LOADSTRING 100
#define CHECK_ID 1001

// Global Variables:
HINSTANCE hInst; // current instance
TCHAR szTitle[MAX_LOADSTRING]; // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING]; // the main window class name

// Forward declarations of functions included in this code module:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);

// TODO: Place code here.
MSG msg;
HACCEL hAccelTable;

// Initialize global strings
LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadString(hInstance, IDC_ECHECK, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);

// Perform application initialization:
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}

hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_ECHECK));

// Main message loop:
while (GetMessage(&msg, NULL, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}

return (int) msg.wParam;
}



//
// FUNCTION: MyRegisterClass()
//
// PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEX wcex;

wcex.cbSize = sizeof(WNDCLASSEX);

wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_ECHECK));
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = MAKEINTRESOURCE(IDC_ECHECK);
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

return RegisterClassEx(&wcex);
}

//
// FUNCTION: InitInstance(HINSTANCE, int)
//
// PURPOSE: Saves instance handle and creates main window
//
// COMMENTS:
//
// In this function, we save the instance handle in a global variable and
// create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
HWND hWnd;

hInst = hInstance; // Store instance handle in our global variable

hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

if (!hWnd)
{
return FALSE;
}

ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);

return TRUE;
}

//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_COMMAND - process the application menu
// WM_PAINT - Paint the main window
// WM_DESTROY - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
static HWND hcheckbox;
switch (message)
{
case WM_CREATE:
hcheckbox=CreateWindowEx(NULL, L"BUTTON", L"Check me", WS_VISIBLE | BS_CHECKBOX | WS_CHILD, 10,10, 300,30, hWnd, (HMENU)CHECK_ID, hInst, NULL);

break;
case WM_COMMAND:
wmId = LOWORD(wParam);
wmEvent = HIWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
case CHECK_ID:
//MessageBox(hWnd, L"Checked", L"Yes", MB_OK);
int checked;
checked = IsDlgButtonChecked(hWnd, CHECK_ID);
if(checked!=BST_CHECKED) {
CheckDlgButton(hWnd, CH

As far as I can see, the code fragment for WM_COMMAND case is wrong. It ends with opening bracket '{' under "if", with another case underneath. You have to remove it. Switch statement should come with some cases each ending with "break;". Just re-factor your code. Your case WM_COMMAND can have a block ending with "break". Inside this block, you can have another switch based on, say, lower word of lParam. Better yet, at this point call a separate function which processes WM_COMMAND depending in wParam and lParam you can pass to it.
—SA