Calculate with values from pointers?

I really need some help with my program for calculating BMI (Body Mass Index)
(Full program at the bottom)
Here is the part of my program where the errors are:
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case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);

		// GET TEXT
		if (HIWORD(wParam) == ID_BUTTON)
			{
			char szCopyh[20];
			char szCopyv[20];
			GetWindowText(hwndTexth, szCopyh, sizeof (szCopyh));
			GetWindowText(hwndTextv, szCopyv, sizeof (szCopyv));
			char result[20] = (szCopyv/((szCopyh/100)*(szCopyh/100)));
			SetWindowText(hwndshow, result);
		}


This is a piece of my program.
1. hwndTexth = Textbox Input 1
2. hwndTextv = Textbox Input 2
3. hwndshow = Textbox Output

HOW CAN I CALCULATE WITH THE 2 INPUTS FROM THE TEXTBOXES?

One of the errors:
error C2296: '/' : illegal, left operand has type 'char [20]'

I think the other errors is because i can't add two pointers.

FULL PROGRAM:
Sorry for the: // Danish notes
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// BMI.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "BMI.h"
#include <iostream>
using namespace std;

enum eHandleWindows{

	ID_BUTTON // Button box
	

}eHandle;

#define MAX_LOADSTRING 100

// 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(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     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_BMI, szWindowClass, MAX_LOADSTRING);
	MyRegisterClass(hInstance);

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

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

	// 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.
//
//  COMMENTS:
//
//    This function and its usage are only necessary if you want this code
//    to be compatible with Win32 systems prior to the 'RegisterClassEx'
//    function that was added to Windows 95. It is important to call this function
//    so that the application will get 'well formed' small icons associated
//    with it.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
	WNDCLASSEX wcex;

	wcex.cbSize = sizeof(WNDCLASSEX);

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

	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;

   hWnd = CreateWindow(szWindowClass, szTitle, WS_BORDER | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX,
      GetSystemMetrics(SM_CXSCREEN)/2-150, GetSystemMetrics(SM_CYSCREEN)/2-200, 300, 400, 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
//
//

//
	HWND hwndTexth; // Textbox CM name
	HWND hwndTextv;// Textbox KG name
	HWND hwndshow; // Showbox name
	HWND hwndbtn; // KNAP name
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	int wmId, wmEvent;

	switch (message)
	{
	// TEXTBOX
	case WM_CREATE:{
		// HØJDE
		hwndTexth = CreateWindow(
                               TEXT("edit"),
                               TEXT(""),
                               WS_VISIBLE | WS_CHILD | WS_BORDER | ES_AUTOHSCROLL,
                               150,30,
                               100,20,
                               hWnd,
                               (HMENU) NULL,
                               NULL,
                               NULL
                            ); 
			
		// VÆGT
		hwndTextv = CreateWindow(
                               TEXT("edit"),
                               TEXT(""),
                               WS_VISIBLE | WS_CHILD | WS_BORDER | ES_AUTOHSCROLL,
                               150,100,
                               100,20,
                               hWnd,
                               (HMENU) NULL,
                               NULL,
                               NULL
                            ); 
		//KNAP
		hwndbtn = CreateWindow(
                               TEXT("button"),
                               TEXT("Vis BMI"),
                               WS_VISIBLE | WS_CHILD | WS_BORDER,
                               100,150,
                               100,20,
                               hWnd,
                               (HMENU) ID_BUTTON,
                               NULL,
                               NULL
                            ); 

		// RESULTAT
		hwndshow = CreateWindow(
                               TEXT("static"),
                               TEXT(""),
                               WS_VISIBLE | WS_CHILD | WS_BORDER | ES_AUTOHSCROLL,
                               150,200,
                               100,20,
                               hWnd,
                               (HMENU) NULL,
                               NULL,
                               NULL
                            ); 

		break;
				   }
	

	case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);

		// GET TEXT
		if (HIWORD(wParam) == ID_BUTTON)
			{
			char szCopyh[20];
			char szCopyv[20];
			GetWindowText(hwndTexth, szCopyh, sizeof (szCopyh));
			GetWindowText(hwndTextv, szCopyv, sizeof (szCopyv));
			char result[20] = (szCopyv/((szCopyh/100)*(szCopyh/100)));
			SetWindowText(hwndshow, result);
		}
		// Parse the menu selections:
		switch (wmId)
		{
		case IDM_ABOUT:
			::MessageBox(hWnd, _T("Lavet af FlazZ") , _T("Om"), MB_OK);
			break;
		case IDM_EXIT:
			DestroyWindow(hWnd);
			break;
		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
		}
		break;
	case WM_PAINT:
		{
        PAINTSTRUCT ps;
		HDC hdc; 
		hdc = BeginPaint(hWnd, &ps);
		TextOut(hdc, 52,32, _T("Din højde i cm:"),15);
		TextOut(hdc, 52,102, _T("Din vægt i kg:"),14);
		TextOut(hdc, 60,202, _T("Din BMI:"),8);
		EndPaint(hWnd, &ps);
		}
		break;
	case WM_DESTROY:
		PostQuitMessage(0);
		break;
	default:
		return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
	UNREFERENCED_PARAMETER(lParam);
	switch (message)
	{
	case WM_INITDIALOG:
		return (INT_PTR)TRUE;

	case WM_COMMAND:
		if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
		{
			EndDialog(hDlg, LOWORD(wParam));
			return (INT_PTR)TRUE;
		}
		break;
	}
	return (INT_PTR)FALSE;
}
Can you explain what you're trying to do with this piece of code so we can correct it.
 
char result[20] = (szCopyv/((szCopyh/100)*(szCopyh/100)));

If you want to do a calculation with a number that's held in a string, you need to extract it to a numeric type so you can math with it. Then convert the result back into a string so it can be displayed.

So, with code:
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if (HIWORD(wParam) == ID_BUTTON)
{
	char szCopyh[20];
	char szCopyv[20];
	GetWindowText(hwndTexth, szCopyh, sizeof (szCopyh));
	GetWindowText(hwndTextv, szCopyv, sizeof (szCopyv));

	// convert to numbers
	double h = atof(szCopyh);
	double v = atof(szCopyv);

	// do some calculation
	double r = v/(100.0 * h);

	// convert back to a string for display
	char result[20];
	snprintf(result, sizeof(result), "%f", r); 

//	char result[20] = (szCopyv/((szCopyh/100)*(szCopyh/100)));
	SetWindowText(hwndshow, result);
}
Can you explain what you're trying to do with this piece of code so we can correct it.

I was trying to calculate with the inputs directly.

But thanks for the code, that solved my problem.
But this time i get an error in line 17:
error C3861: 'snprintf': identifier not found
The line:
snprintf(result, sizeof(result), "%f", r);

EDIT:
Oh, my bad!
I forgot to:
#define snprintf _snprintf
and
#include <stdio.h>

Thanks for the help!
Last edited on
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