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:
 ``1234567891011121314`` ``````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
 ``123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279`` ``````// BMI.cpp : Defines the entry point for the application. // #include "stdafx.h" #include "BMI.h" #include 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:
 ``123456789101112131415161718192021`` ``````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:
`#define snprintf _snprintf `
`#include <stdio.h> `