from tkinter import Tk, Entry, Button, Label, messagebox

def calculate():
    try:
        a = float(entry_a.get())
        b = float(entry_b.get())
        operation = entry_operation.get()

        if operation == '+':
            result = a + b
        elif operation == '-':
            result = a - b
        elif operation == '*':
            result = a * b
        elif operation == '/':
            result = a / b

        entry_result.delete(0, 'end')
        entry_result.insert('end', str(result))
    except ValueError:
        messagebox.showerror('Error', 'Invalid input')

def exit_program():
    if messagebox.askyesno('Exit', 'Are you sure you want to exit?'):
        root.destroy()

root = Tk()

label_a = Label(root, text='a:')
label_a.grid(row=0, column=0)
entry_a = Entry(root)
entry_a.grid(row=0, column=1)

label_operation = Label(root, text='Operation:')
label_operation.grid(row=1, column=0)
entry_operation = Entry(root)
entry_operation.grid(row=1, column=1)

label_b = Label(root, text='b:')
label_b.grid(row=2, column=0)
entry_b = Entry(root)
entry_b.grid(row=2, column=1)

button_calculate = Button(root, text='Calculate', command=calculate)
button_calculate.grid(row=3, column=0)

label_result = Label(root, text='Result:')
label_result.grid(row=4, column=0)
entry_result = Entry(root)
entry_result.grid(row=4, column=1)

button_exit = Button(root, text='Exit', command=exit_program)
button_exit.grid(row=5, column=0)

root.mainloop()