Task: GUI enabling_disabling of controls

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

#define MIN_VALUE    0
#define MAX_VALUE   10

BOOL CALLBACK DlgProc( HWND hwnd, UINT msg, WPARAM wPar, LPARAM lPar );
void Increment( HWND hwnd );
void Decrement( HWND hwnd );
void SetControlsState( HWND hwnd );

int WINAPI WinMain( HINSTANCE hInst, HINSTANCE hPInst, LPSTR cmdLn, int show ) {
    return DialogBox( hInst, MAKEINTRESOURCE(IDD_DLG), NULL, DlgProc );
}

BOOL CALLBACK DlgProc( HWND hwnd, UINT msg, WPARAM wPar, LPARAM lPar ) {
    switch( msg ) {

        case WM_INITDIALOG:
            srand( GetTickCount() );
            SetDlgItemInt( hwnd, IDC_INPUT, 0, FALSE );
            break;

        case WM_COMMAND:
            switch( LOWORD(wPar) ) {
                case IDC_INCREMENT:
                    Increment( hwnd );
                    break;
                case IDC_DECREMENT:
                    Decrement( hwnd );
                    break;
                case IDC_INPUT:
                    
                    
                    if( HIWORD(wPar) == EN_CHANGE ) SetControlsState( hwnd );
                    break;
                case IDC_QUIT:
                    SendMessage( hwnd, WM_CLOSE, 0, 0 );
                    break;
                default: ;
            }
            break;

        case WM_CLOSE: {
            int reply = MessageBox( hwnd,
                "Do you really want to quit?",
                "Quit confirmation", MB_ICONQUESTION|MB_YESNO );
            if( reply == IDYES )
                EndDialog( hwnd, 0 );
            } break;

        default: ;
    }

    return 0;
}

void Increment( HWND hwnd ) {
    UINT n = GetDlgItemInt( hwnd, IDC_INPUT, NULL, FALSE );

    if( n < MAX_VALUE ) {
        SetDlgItemInt( hwnd, IDC_INPUT, ++n, FALSE );
        SetControlsState( hwnd );
    }
}

void Decrement( HWND hwnd ) {
    UINT n = GetDlgItemInt( hwnd, IDC_INPUT, NULL, FALSE );

    if( n > MIN_VALUE ) {
        SetDlgItemInt( hwnd, IDC_INPUT, --n, FALSE );
        SetControlsState( hwnd );
    }
}

void SetControlsState( HWND hwnd ) {
    UINT n = GetDlgItemInt( hwnd, IDC_INPUT, NULL, FALSE );
    EnableWindow( GetDlgItem(hwnd,IDC_INCREMENT), n<MAX_VALUE );
    EnableWindow( GetDlgItem(hwnd,IDC_DECREMENT), n>MIN_VALUE );
}




Go: package main

import (
    "github.com/gotk3/gotk3/gtk"
    "log"
    "math/rand"
    "strconv"
    "time"
)

func validateInput(window *gtk.Window, str string) (int64, bool) {
    i, err := strconv.ParseInt(str, 10, 64)
    if err != nil {
        dialog := gtk.MessageDialogNew(
            window,
            gtk.DIALOG_MODAL,
            gtk.MESSAGE_ERROR,
            gtk.BUTTONS_OK,
            "Invalid value",
        )
        dialog.Run()
        dialog.Destroy()
        return 0, false
    }
    return i, true
}

func check(err error, msg string) {
    if err != nil {
        log.Fatal(msg, err)
    }
}

func processState(i int64, entry *gtk.Entry, ib, db *gtk.Button) {
    if i == 0 {
        entry.SetSensitive(true)
    } else {
        entry.SetSensitive(false)
    }
    if i < 10 {
        ib.SetSensitive(true)
    } else {
        ib.SetSensitive(false)
    }
    if i > 0 {
        db.SetSensitive(true)
    } else {
        db.SetSensitive(false)
    }
}

func main() {
    rand.Seed(time.Now().UnixNano())
    gtk.Init(nil)

    window, err := gtk.WindowNew(gtk.WINDOW_TOPLEVEL)
    check(err, "Unable to create window:")
    window.SetTitle("Rosetta Code")
    window.SetPosition(gtk.WIN_POS_CENTER)
    window.Connect("destroy", func() {
        gtk.MainQuit()
    })

    box, err := gtk.BoxNew(gtk.ORIENTATION_HORIZONTAL, 1)
    check(err, "Unable to create box:")
    box.SetBorderWidth(1)

    label, err := gtk.LabelNew("Value:")
    check(err, "Unable to create label:")

    entry, err := gtk.EntryNew()
    check(err, "Unable to create entry:")
    entry.SetText("0") 
    entry.SetSensitive(true)

    
    ib, err := gtk.ButtonNewWithLabel("Increment")
    check(err, "Unable to create increment button:")
    ib.SetSensitive(true)

    
    db, err := gtk.ButtonNewWithLabel("Decrement")
    check(err, "Unable to create decrement button:")
    db.SetSensitive(false)

    entry.Connect("activate", func() {
        
        str, _ := entry.GetText()
        i, ok := validateInput(window, str)
        if !ok {
            entry.SetText("0")
        }
        processState(i, entry, ib, db)
    })

    ib.Connect("clicked", func() {
        
        str, _ := entry.GetText()
        i, _ := validateInput(window, str)
        i++
        entry.SetText(strconv.FormatInt(i, 10))
        processState(i, entry, ib, db)
    })

    db.Connect("clicked", func() {
        
        str, _ := entry.GetText()
        i, _ := validateInput(window, str)
        i--
        entry.SetText(strconv.FormatInt(i, 10))
        processState(i, entry, ib, db)
    })

    box.PackStart(label, false, false, 2)
    box.PackStart(entry, false, false, 2)
    box.PackStart(ib, false, false, 2)
    box.PackStart(db, false, false, 2)
    window.Add(box)

    window.ShowAll()
    gtk.Main()
}