Problems with a window event callback function C++ - c++

Question

I am currently facing issues when trying to compile my code that contains this WinProc function which is being used to process messages from our program. For example if a WM_DESTROY message is received via windows I want it to call PostQuitMessage(0) to signal Windows that the application has made a request to quit. Which will cause the WM_QUIT message to cause the WinMain to exit.
I have only been learning C++ a few weeks and don't have the experience or knowledge to fix this and would appreciate any help. I have looked around but so far I cannot find any solutions. I'm pretty new to this so I may have missed something really obvious.
LRESULT WINAPI WinProc (hWnd, msg, UNIT msg, WPARAM wParam, LPARAM lParam )
{
switch( msg )
{
case WM_DESTROY;
// Tell windows to kill the program
PostQuitMessage(0);
return 0;
}
return DefWindowProc (hWnd, msg, wParam, lParam );
}
Below is the errors I experience wit the code that I have provided.
error: 'LRESULT WinProc' redeclared as different kind of symbol
error: previous declaration of 'LRESULT WinProc(HWND__*, UINT, WPARAM, LPARAM)'
error: 'hWnd' was not declared in this scope
error: 'msg' was not declared in this scope
error: 'UNIT' was not declared in this scope
Any help would be greatly appreciated.
Thanks

Answer 1

In the function declaration
LRESULT WINAPI WinProc (hWnd, msg, UNIT msg, WPARAM wParam, LPARAM lParam )
you forgot to set type specifiers for the first two parameters hWnd and msg
There must be
LRESULT WINAPI WinProc ( HWND hWnd, UNIT msg, WPARAM wParam, LPARAM lParam )
Also the label has to be followed by a colon while you placed a semicolon
case WM_DESTROY;

Answer 2

try using the callback calling convention instead of winapi
https://msdn.microsoft.com/en-us/library/windows/desktop/ms633570(v=vs.85).aspx
also note the usage of " : " instead of " ; " on switch statement , also specify a type before the handle and message arguments
LRESULT CALLBACK WinProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch( msg )
{
case WM_DESTROY:
// Tell windows to kill the program
PostQuitMessage(0);
return 0;
}
return DefWindowProc (hWnd, msg, wParam, lParam );
}

Answer 3

LRESULT CALLBACK WndProc( HWND, UINT, WPARAM, LPARAM )
This should be the function declaration. Your case has a ";" semicolon instead of a ":" colon.
Besides this, I don't see any problems. Try this:
LRESULT CALLBACK WndProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
switch( msg )
{
case WM_DESTROY:
// Tell windows to kill the program
PostQuitMessage(0);
return 0;
}
return DefWindowProc (hWnd, msg, wParam, lParam );
}