C++ many errors when defining string - c++

Question

Hello i am learning C++ and i have errors while making VISUAL APP NOT CONSOLE
My problem is at the string Num1 = "0";
Please explain to me why this is happening?
The string is 0 because i want to make calculator so i need to make Num1 + "TheClicked number"
<script>
#include <windows.h>
/* Declare Windows procedure */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
/* Make the class name into a global variable */
char szClassName[ ] = "Andrey App";
int WINAPI WinMain (HINSTANCE hThisInstance,
HINSTANCE hPrevInstance,
LPSTR lpszArgument,
int nFunsterStil)
{
HWND hwnd; /* This is the handle for our window */
MSG messages; /* Here messages to the application are saved */
WNDCLASSEX wincl; /* Data structure for the windowclass */
/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure; /* This function is called by windows */
wincl.style = CS_DBLCLKS; /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);
/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
wincl.lpszMenuName = NULL; /* No menu */
wincl.cbClsExtra = 0; /* No extra bytes after the window class */
wincl.cbWndExtra = 0; /* structure or the window instance */
/* Use Windows's default color as the background of the window */
wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
return 0;
/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
0, /* Extended possibilites for variation */
szClassName, /* Classname */
"Andrey App", /* Title Text */
WS_OVERLAPPEDWINDOW, /* default window */
CW_USEDEFAULT, /* Windows decides the position */
CW_USEDEFAULT, /* where the window ends up on the screen */
544, /* The programs width */
375, /* and height in pixels */
HWND_DESKTOP, /* The window is a child-window to desktop */
NULL, /* No menu */
hThisInstance, /* Program Instance handler */
NULL /* No Window Creation data */
);
/* Make the window visible on the screen */
ShowWindow (hwnd, nFunsterStil);
/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&messages, NULL, 0, 0))
{
/* Translate virtual-key messages into character messages */
TranslateMessage(&messages);
/* Send message to WindowProcedure */
DispatchMessage(&messages);
}
/* The program return-value is 0 - The value that PostQuitMessage() gave */
return messages.wParam;
}
/* This function is called by the Windows function DispatchMessage() */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message) /* handle the messages */
{
string Num1 = "0";
case WM_CREATE:
{
CreateWindow(TEXT("button"), TEXT("Beep"),
WS_VISIBLE | WS_CHILD ,
20, 50, 80, 25,
hwnd, (HMENU) 1, NULL, NULL);
CreateWindow(TEXT("button"), TEXT("2"),
WS_VISIBLE | WS_CHILD ,
120, 50, 30, 30,
hwnd, (HMENU) 2, NULL, NULL);
CreateWindow(L"STATIC", Num1,
WS_CHILD | WS_VISIBLE | SS_LEFT,
20, 20, 300, 230,
hwnd, (HMENU) 1, NULL, NULL);
break;
}
case WM_COMMAND:
{
if (LOWORD(wParam) == 1) {
Beep(40, 50);
}
if (LOWORD(wParam) == 2) {
if(Num1 == 0){
Num1 = 2;
}
else{
Num1 + "2";
}
}
break;
}
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}

Answer 1

Here's how it should look:
//At the top of your .cpp file
#include<string>
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
static std::string Num1 = "0"; /* static string created once and keeps it contents for each function call */
switch (message) /* handle the messages */
{
case WM_CREATE:
{
CreateWindow(TEXT("button"), TEXT("Beep"),
WS_VISIBLE | WS_CHILD ,
20, 50, 80, 25,
hwnd, (HMENU) 1, NULL, NULL);
CreateWindow(TEXT("button"), TEXT("2"),
WS_VISIBLE | WS_CHILD ,
120, 50, 30, 30,
hwnd, (HMENU) 2, NULL, NULL);
///CreateWindow takes a LPCSTR as second arg, which is wchar_t under the covers, so need to convert
std::wstring wstr(Num1.begin(), Num1.end());
CreateWindow(L"STATIC", wstr.c_str(), //.c_str() returns a const char*
WS_CHILD | WS_VISIBLE | SS_LEFT,
20, 20, 300, 230,
hwnd, (HMENU) 1, NULL, NULL);
break;
}
case WM_COMMAND:
{
if (LOWORD(wParam) == 1) {
Beep(40, 50);
}
if (LOWORD(wParam) == 2) {
if(Num1 == "0"){ //Num1 is a string, so you should check a string
Num1 = "2";
}
else{
Num1 += "2";
}
}
break;
}
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}