from tkinter import *



root = Tk()
root.title('Simple Calculator')
e = Entry(root, width=35, borderwidth=5)
e.grid(row=0, column=0, columnspan=3, padx=10, pady=10)

def button_click(number):
    currentNumber = e.get()
    e.delete(0, END)
    e.insert(0, str(currentNumber) + str(number))

def add(operator):
    global firstNumber 
    global sign
    firstNumber = int(e.get()) 
    sign = operator
    e.delete(0, END)

def subtract(operator):
    global firstNumber
    global sign
    firstNumber = int(e.get()) 
    sign = operator
    e.delete(0, END)

def multiply(operator):
    global firstNumber
    global sign
    firstNumber = int(e.get()) 
    sign = operator
    e.delete(0, END)

def divide(operator):
    global firstNumber
    global sign
    firstNumber = int(e.get()) 
    sign = operator
    e.delete(0, END)

def equal():
    global firstNumber
    global sign
    secondNumber = int(e.get())
    e.delete(0, END)
    if sign == '+':
        e.insert(0, firstNumber + secondNumber)
    elif sign == '-':
        e.insert(0, firstNumber - secondNumber)
    elif sign == '/':
        e.insert(0, firstNumber / secondNumber)
    elif sign == '*':
        e.insert(0, firstNumber * secondNumber)
    firstNumber = 0
    sign = []

def clear():
    e.delete(0, END)

# Define buttons
button_1 = Button(root, text='1', padx = 40, pady = 20, command=lambda : button_click(1))
button_2 = Button(root, text='2', padx = 40, pady = 20, command=lambda : button_click(2))
button_3 = Button(root, text='3', padx = 40, pady = 20, command=lambda : button_click(3))
button_4 = Button(root, text='4', padx = 40, pady = 20, command=lambda : button_click(4))
button_5 = Button(root, text='5', padx = 40, pady = 20, command=lambda : button_click(5))
button_6 = Button(root, text='6', padx = 40, pady = 20, command=lambda : button_click(6))
button_7 = Button(root, text='7', padx = 40, pady = 20, command=lambda : button_click(7))
button_8 = Button(root, text='8', padx = 40, pady = 20, command=lambda : button_click(8))
button_9 = Button(root, text='9', padx = 40, pady = 20, command=lambda : button_click(9))
button_0 = Button(root, text='0', padx = 40, pady = 20, command=lambda : button_click(0))

button_add = Button(root, text='+', padx = 39, pady = 20, command=lambda : add('+'))
button_equal = Button(root, text='=', padx = 86, pady = 20, command=equal)
button_clear = Button(root, text='Clear', padx = 77, pady = 20, command=clear)

button_sub = Button(root, text='-', padx = 39, pady = 20, command=lambda : subtract('-'))
button_mul = Button(root, text='*', padx = 39, pady = 20, command=lambda : multiply('*'))
button_div = Button(root, text='/', padx = 39, pady = 20, command=lambda : divide('/'))

# Put buttons on GUI
button_1.grid(row=3, column=0)
button_2.grid(row=3, column=1)
button_3.grid(row=3, column=2)

button_4.grid(row=2, column=0)
button_5.grid(row=2, column=1)
button_6.grid(row=2, column=2)

button_7.grid(row=1, column=0)
button_8.grid(row=1, column=1)
button_9.grid(row=1, column=2)

button_0.grid(row=4, column=0)
button_add.grid(row=5, column=0)
button_equal.grid(row=5, column=1, columnspan=2)
button_clear.grid(row=4, column=1, columnspan=2)

button_sub.grid(row=6, column=0)
button_mul.grid(row=6, column=1)
button_div.grid(row=6, column=2)

# running the main loop.
root.mainloop()