Win32 API child window flicker - c

Question

I'm new to the Win32 API and can't understand why all of my child windows are flickering so much whenever I input something into them. Does anyone know why it is flickering? Below is what I coded; it doesn't seem to work as intended. Even though I'm sure I handled all of my handles correctly and used the pointers properly throughout the code.
#include <windows.h>
#include <string.h>
#include <stdlib.h>
#define CONVERT_TAX 1
LRESULT CALLBACK WindowProcedure(HWND,UINT,WPARAM,LPARAM);
void AddMenus(HWND hWnd);
void AddControls(HWND hWnd);
int TaxConversion(int TaxRate);
HWND hOut;
HWND hTax;
int main(HINSTANCE hInst, HINSTANCE vPrevInst,LPSTR args, int ncmdshow){
WNDCLASSW wc ={};
wc.hIcon=LoadIcon(NULL, IDI_APPLICATION); //The icon handle for the window class. LoadIcon(NULL, IDI_APPLICATION) loads the default application icon.
wc.cbWndExtra=0; //The number of extra bytes to allocate for each individual window. Do not confuse this with cbClsExtra, which is common to all instances. This is often 0.
wc.cbClsExtra=0; //The number of extra bytes to allocate for the window class. For most situations, this member is 0.
wc.style=0; //
wc.hbrBackground=(HBRUSH)COLOR_WINDOW; //A handle to the background brush. GetStockObject (WHITE_BRUSH) gives a handle to a white brush. The return value must be cast because GetStockObject returns a generic object.
wc.hCursor=LoadCursor(NULL,IDC_ARROW); //The cursor handle for the window class. LoadCursor(NULL, IDC_ARROW) loads the default cursor.
wc.hInstance=hInst; //The instance handle. Just assign the hInst argument in WinMain to this field.
wc.lpszClassName=L"myWindowClass"; //The class name that identifies this window class structure. In this example, the CLSNAME global variable stores the window class name.
wc.lpfnWndProc=WindowProcedure; //Stores the address of the window procedure, a function that handles events for all windows that are instances of this window class.
if(!RegisterClassW(&wc))
return -1;
CreateWindowW(L"myWindowClass",L"My Window",WS_OVERLAPPEDWINDOW|WS_VISIBLE,500,500,500,500,NULL,NULL,NULL,NULL);
MSG msg = {0};
while(GetMessage(&msg,NULL,0,0)){
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
LRESULT CALLBACK WindowProcedure(HWND hWnd,UINT msg,WPARAM wp,LPARAM lp){ //Procedures for Events
switch(msg){
case WM_COMMAND:
switch(wp){
case CONVERT_TAX:
char Tax[100];
GetWindowText(hTax,Tax,100);
SetWindowText(hOut,Tax);
break;
}
case WM_CREATE:
AddControls(hWnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProcW(hWnd,msg,wp,lp);
}
return 0;
}
void AddControls(HWND hWnd){
CreateWindowW(L"Static",L"Enter Tax Rate",WS_CHILD|WS_VISIBLE,1,1,90,90,hWnd,0,0,0);
hTax=CreateWindowW(L"Edit",L"",WS_CHILD|WS_BORDER|WS_VISIBLE,1,92,90,90,hWnd,0,0,0);
CreateWindowW(L"Button",L"Find Amount",WS_CHILD|WS_BORDER|WS_VISIBLE,1,183,90,90,hWnd,(HMENU)CONVERT_TAX,0,0);
hOut=CreateWindowW(L"Edit",L"",WS_CHILD|WS_BORDER|WS_VISIBLE,1,267,90,90,hWnd,0,0,0);
}

Answer 1

I see two mistakes in your code:
when setting wc.hbrBackground, you must add +1 to the color value, per the documentation:
https://learn.microsoft.com/en-us/windows/win32/api/winuser/ns-winuser-wndclassw
hbrBackground
Type: HBRUSH
A handle to the class background brush. This member can be a handle to the physical brush to be used for painting the background, or it can be a color value. A color value must be one of the following standard system colors (the value 1 must be added to the chosen color)...
wc.hbrBackground=(HBRUSH)(COLOR_WINDOW+1); // <-- add +1
your WM_COMMAND handler is missing a break after the switch block, so every command message received will fall through into your WM_CREATE handler, thus creating more and more child controls.
case WM_COMMAND:
switch(wp){
case CONVERT_TAX:
char Tax[100];
GetWindowText(hTax,Tax,100);
SetWindowText(hOut,Tax);
break;
}
break; // <-- add this