Calculate data from string like "1 + 1" = 2 in WinAPI C [duplicate] - c

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parsing math expression in c++
(6 answers)
Closed 1 year ago.
I'm currently trying to make pure WinAPI calculator that will have:
1 result textbox (where all data would be displayed)
some buttons like plus, minus, 1, 2 etc (on click, these will append text like 1,+,2 etc to Result textbox)
So now, suppose the result textbox contains string like 1 + 1, 7 / 2, 2 * 2, 8 - 8 etc, How can I invoke these strings to return data like 2, 3.5, 4, 0 respectively?
Is there any standard api in WinAPI by which I can invoke the calculation inside a string? Or do I need to make my own?
I'm using C WinAPI.
And here I got manage to complete UI and append text via buttons. Please see code:
#include <windows.h>
int IDC_result = 16;
int w = 50;
int h = 50;
void DrawButton(HWND hwnd, const char* Text, int x, int y, int code)
{
CreateWindowW(TEXT("button"), (LPCWSTR)Text, WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON, x, y, w, h, hwnd, (HMENU)code, NULL, NULL);
}
const char* texts[] =
{
"7","8","9","/",
"4","5","6","*",
"1","2","3","-",
"0",".","=","+"
};
int textsLenght = (int)(sizeof(texts) / sizeof(texts[0]));
HWND RESULTS;
void DrawControls(HWND hwnd)
{
int TotalColms = 4;
RESULTS = CreateWindowEx(WS_EX_TRANSPARENT, TEXT("Edit"), TEXT(""), WS_CHILD | WS_VISIBLE | SS_LEFT | WS_SYSMENU, w * 1, h - 25, w * TotalColms, h - 30, hwnd, (HMENU)IDC_result, NULL, NULL);
int colm = 1;
int row = 1;
for(int text = 0; text < textsLenght; text++)
{
DrawButton(hwnd,texts[text],w * colm,h * row,text);
if (textsLenght / colm == TotalColms)
{
colm = 0;
row++;
}
colm++;
}
}
void appendText(LPARAM Text)
{
int Lenght = GetWindowTextLength(RESULTS);
SendMessageW(RESULTS, EM_SETSEL, Lenght, Lenght);
SendMessageW(RESULTS, EM_REPLACESEL, TRUE, Text);
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_CREATE:
DrawControls(hwnd);
break;
case WM_COMMAND:
{
int no = LOWORD(wParam);
if (no > -1 && no < textsLenght)
{
appendText((LPARAM)texts[no]);
}
break;
}
case WM_DESTROY: PostQuitMessage(0);
default: return DefWindowProc(hwnd, message, wParam, lParam);
}
return 0;
}
int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nCmdShow)
{
MSG msg;
WNDCLASS wc;
HWND hwnd;
ZeroMemory(&wc, sizeof wc);
wc.hInstance = hInstance;
wc.lpszClassName = L"Calculator";
wc.lpfnWndProc = (WNDPROC)WndProc;
wc.style = CS_DBLCLKS | CS_VREDRAW | CS_HREDRAW;
wc.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
if (FALSE == RegisterClass(&wc)) return 0;
hwnd = CreateWindowW(
L"Calculator",L"Calculator"
,WS_OVERLAPPEDWINDOW | WS_VISIBLE,CW_USEDEFAULT,CW_USEDEFAULT,
300,500
,0,0,hInstance,0);
if (NULL == hwnd) return 0;
while (GetMessage(&msg, NULL, 0, 0) > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}
Please comment, if anything unclear.

Answer 1

Is there any standard api in winapi by which we can invoke the
calculation inside a string ? or I need to make my own ?
No there is no standard API for this; you must either make your own, or more practically find a pre-made library for this.
Another option if you want something that "just works even though it's extremely dirty/hacky/insecure" is to find a way to invoke powershell from your app and capture the output.