import tkinter as tk

def click(event):
    global expression
    text = event.widget.cget("text")
    if text == "=":
        try:
            result = str(eval(expression))
            entry_var.set(result)
            expression = result
        except Exception as e:
            entry_var.set("Error")
            expression = ""
            
    elif text == "C":
        expression = ""
        entry_var.set("")
    else:
        expression += text
        entry_var.set(expression)


root = tk.Tk()
root.title("Simple Calculator")
root.geometry("300x400")

expression = ""
entry_var = tk.StringVar()

entry = tk.Entry(root, textvar=entry_var, font="Arial 20", justify="right")
entry.pack(fill="both", ipadx=8, pady=10, padx=10)

button_frame = tk.Frame(root)
button_frame.pack()

buttons = [
    ["7", "8", "9", "/"],
    ["4", "5", "6", "*"],
    ["1", "2", "3", "-"],
    ["0", "C", "=", "+"]
]

for row in buttons:
    frame = tk.Frame(button_frame)
    frame.pack(expand=True, fill="both")
    for btn in row:
        b = tk.Button(frame, text=btn, font="Arial 18", relief="ridge", width=5, height=2)
        b.pack(side="left", expand=True, fill="both")
        b.bind("<Button-1>", click)

root.mainloop()