MessageBox попадает в бесконечный цикл WinApi

int a = 0; 
int b = 1; 
int x = 0; 
////////// 
static BOOL OnCommand(WPARAM wParam, HWND hwnd) 
	{ 
		auto controlID = LOWORD(wParam); 
		auto notification = HIWORD(wParam); 
 
		switch (controlID) 
		{ 
		case IDC_NUMBER1: 
			switch (notification) 
			{ 
			case EN_CHANGE: 
				a = GetDlgItemInt(hwnd, IDC_NUMBER1, &fError, fRelative); 
				return IfClicked(hwnd); 
			} 
			break; 
 
		case IDC_NUMBER2: 
			switch (notification) 
			{ 
			case EN_CHANGE: 
				b = GetDlgItemInt(hwnd, IDC_NUMBER2, &fError, fRelative); 
				return IfClicked(hwnd); 
			}			 
  } 
  ////////// 
  static BOOL ProcessTestRadioButton(int a, int b, HWND hwnd) 
	{ 
		auto checkState = SendMessageW(GetControl(IDC_ARITHMETIC), BM_GETCHECK, 0, 0); 
		if (checkState == BST_CHECKED) 
		{ 
			ArithmeticCalculating(a, b, hwnd); 
		} 
		else 
		{ 
			ComparativeCalculating(a, b, hwnd); 
		} 
		return TRUE; 
	} 
////////////// 
static	BOOL ArithmeticCalculating(int a, int b, HWND hwnd) 
	{ 
		auto testComboBox = GetControl(IDC_COMBO); 
		int selectedIndex = SendMessageW(testComboBox, CB_GETCURSEL, 0, 0); 
 
		switch (selectedIndex) 
		{ 
		case 0: 
			x = a - b; 
			break; 
		case 1: 
			x = a * b; 
			break; 
		case 2: 
			if (b == 0) 
			{ 
				MessageBoxW(_hDialog, L"Error!", L"The Message", MB_OK | MB_ICONSTOP);				 
				return TRUE; 
			} 
			x = a / b; 
			break; 
		case 3: 
			x = a + b; 
			break; 
		} 
		SetDlgItemInt(hwnd, IDC_ANSWER, x, TRUE); 
		return TRUE; 
	}