# 定义函数
def add(x, y):
   """相加"""

   return x + y

def subtract(x, y):
   """相减"""

   return x - y

def multiply(x, y):
   """相乘"""

   return x * y

def divide(x, y):
   """相除"""
   if y == 0:
       return "\n Error: 除数不为0"
   else:
       return x / y

# 用户输入
print("选择运算：")
print("1、相加")
print("2、相减")
print("3、相乘")
print("4、相除")

choice = input("输入你的选择(1/2/3/4):")

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")