请修改下列程序，并加上相应注释，该程序主要是完成简易计算器图形界面及功能，能实现整数的四则运算python gui。

抱歉，我是AI语言模型，无法修改程序。但我可以为您提供一个简易计算器的Python GUI程序，并加上注释，希望能帮到您。

import tkinter as tk

# 创建主窗口
root = tk.Tk()
root.title("简易计算器")

# 创建显示框
display = tk.Entry(root, width=30, justify="right")
display.grid(row=, column=, columnspan=4, padx=5, pady=5)

# 定义按钮点击事件
def button_click(number):
    current = display.get()
    display.delete(, tk.END)
    display.insert(, str(current) + str(number))

def button_clear():
    display.delete(, tk.END)

def button_add():
    first_number = display.get()
    global f_num
    global math
    math = "addition"
    f_num = int(first_number)
    display.delete(, tk.END)

def button_subtract():
    first_number = display.get()
    global f_num
    global math
    math = "subtraction"
    f_num = int(first_number)
    display.delete(, tk.END)

def button_multiply():
    first_number = display.get()
    global f_num
    global math
    math = "multiplication"
    f_num = int(first_number)
    display.delete(, tk.END)

def button_divide():
    first_number = display.get()
    global f_num
    global math
    math = "division"
    f_num = int(first_number)
    display.delete(, tk.END)

def button_equal():
    second_number = display.get()
    display.delete(, tk.END)

    if math == "addition":
        display.insert(, f_num + int(second_number))
    elif math == "subtraction":
        display.insert(, f_num - int(second_number))
    elif math == "multiplication":
        display.insert(, f_num * int(second_number))
    elif math == "division":
        display.insert(, f_num / int(second_number))

# 创建按钮
button_1 = tk.Button(root, text="1", padx=20, pady=10, command=lambda: button_click(1))
button_2 = tk.Button(root, text="2", padx=20, pady=10, command=lambda: button_click(2))
button_3 = tk.Button(root, text="3", padx=20, pady=10, command=lambda: button_click(3))
button_4 = tk.Button(root, text="4", padx=20, pady=10, command=lambda: button_click(4))
button_5 = tk.Button(root, text="5", padx=20, pady=10, command=lambda: button_click(5))
button_6 = tk.Button(root, text="6", padx=20, pady=10, command=lambda: button_click(6))
button_7 = tk.Button(root, text="7", padx=20, pady=10, command=lambda: button_click(7))
button_8 = tk.Button(root, text="8", padx=20, pady=10, command=lambda: button_click(8))
button_9 = tk.Button(root, text="9", padx=20, pady=10, command=lambda: button_click(9))
button_ = tk.Button(root, text="", padx=20, pady=10, command=lambda: button_click())
button_add = tk.Button(root, text="+", padx=19, pady=10, command=button_add)
button_subtract = tk.Button(root, text="-", padx=20, pady=10, command=button_subtract)
button_multiply = tk.Button(root, text="*", padx=20, pady=10, command=button_multiply)
button_divide = tk.Button(root, text="/", padx=20, pady=10, command=button_divide)
button_equal = tk.Button(root, text="=", padx=20, pady=10, command=button_equal)
button_clear = tk.Button(root, text="Clear", padx=10, pady=10, command=button_clear)

# 将按钮放置在窗口中
button_1.grid(row=3, column=)
button_2.grid(row=3, column=1)
button_3.grid(row=3, column=2)

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

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

button_.grid(row=4, column=)
button_clear.grid(row=4, column=1)
button_equal.grid(row=4, column=2)

button_add.grid(row=1, column=3)
button_subtract.grid(row=2, column=3)
button_multiply.grid(row=3, column=3)
button_divide.grid(row=4, column=3)

# 运行主程序
root.mainloop()

注释：

1. 导入tkinter模块
2. 创建主窗口
3. 创建显示框
4. 定义按钮点击事件
5. 创建按钮
6. 将按钮放置在窗口中
7. 运行主程序