练习（常看常新，锻炼思维能力）

简易加减法：
def add(x,y): #相加
return x+y
def sub(x,y): #相减
return x-y
def mul(x,y): #相乘
return x*y
def div(x,y): #相除
return x/y

print("请选择想要进行的运算")
print("1,相加")
print("2,相减")
print("3,相乘")
print("4,相除")

choice=int(input("请输入你要的选择:"))

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

if choice == 1:
print(num1,"+",num2,"=",add(num1,num2))
elif choice == 2:
print(num1,"-",num2,"=",sub(num1,num2))
elif choice == 3:
print(num1,"*",num2,"=",mul(num1,num2))
elif choice == 4:
print(num1,"/",num2,"=",div(num1,num2))
else:
print("算式方法选择错误")