def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    return x / y
while True:
    print("选择运算符：")
    print("1、相加")
    print("2、相减")
    print("3、相乘")
    print("4、相除")
    print("N/n、退出")

    choice = input("请输入你的选择(1/2/3/4):")

    if choice == 'n':
        exit()

    num1 = int(input("输入第一个数字："))
    num2 = int(input("输入第二个数字："))

    if choice == '1':
        print(num1, "+", num2, "=",add(num1, num2) )

    elif choice == '2':
        print(num1, "-", num2, "=",subtract(num1, num2) )

    elif choice == '3':
        print(num1, "*", num2, "=",multiply(num1, num2) )

    elif choice == '4':
        print(num1, "/", num2, "=",divide(num1, num2) )

    else:
        print("非法输入")