I'm making a basic calculator with a C interface with the help of the Win32 API. I've already done the graphic part (I'll leave a screenshot below) and now I need to finish the code.

I could already add text to the Edit Control using buttons. I want that when selecting buttons 1 and 2, the number 12 is typed.

The problem is that when doing so, one number is overwriting another. If I select button 1 and then 2, the number 1 is written, then it is erased and 2 is written.

Do you know how I can fix it? I would also like to know how I can save the data that is inside the Edit control in a variable and then do operations with it.

Excuse me if these are somewhat basic things, I am just starting out with Win32 API. I leave you what I have of the code, thank you very much :)

#include <windows.h>
#include "resource.h"

HWND text;
BOOL CALLBACK mycallback(HWND window, UINT message, WPARAM wParam, LPARAM lParam) {
    
    switch (message) {
    case WM_CLOSE: {
        DestroyWindow(window);
        break;
    }
    case WM_DESTROY: {
        PostQuitMessage(0);
        break;
    }
    case WM_INITDIALOG:
    {
        text = GetDlgItem(window, IDC_EDIT1);
        break;
    }
    case WM_COMMAND:
        switch (LOWORD(wParam))
        {
        case IDC_BUTTON1:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"1");
            break;          
        }
        case IDC_BUTTON2:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"2");
            break;
        }
        case IDC_BUTTON3:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"3");
            break;
        }
        case IDC_BUTTON4:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"4");
            break;
        }
        case IDC_BUTTON5:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"5");
            break;
        }
        case IDC_BUTTON6:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"6");
            break;
        }
        case IDC_BUTTON7:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"7");
            break;
        }
        case IDC_BUTTON8:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"8");
            break;
        }
        case IDC_BUTTON9:
        {
            SendMessage(text, WM_SETTEXT, 0, (LPARAM)"9");
            break;
        }
        case IDC_BUTTON10:
        {
            SendMessage(text, WM_SETTEXT, 0,(LPARAM)"0");
            break;
        }
        }
    }
    return false;
}

int WINAPI WinMain(HINSTANCE a, HINSTANCE b, LPSTR c, int d) {
    DialogBox(a, MAKEINTRESOURCE(IDD_DIALOG1), NULL, mycallback);
    return 0;
}

CodePudding user response：

The simplest way would be to get the text of the control first, append a new digit to it, and then set it.

See GetWindowText and SetWindowText

CodePudding user response：

You could ask for the current text using GetWindowText, append the new text, and follow up with another call to SetWindowText.

Or simply use the Edit control's built-in functionality, and send it an EM_REPLACESEL message. If there is no selection, the new text is inserted at the current caret position.

Reading text back into a variable is best handled in response to an EN_CHANGE notification.