改写简单计算器，利用循环结构使得简单计算器在一次运行后可以重复多次使用

loop = 1
choice = 0
while loop == 1:
    print ("Welcome to calculator.py")
    print ("your options are:")
    print (" ")
    print ("1) Addition")
    print ("2) Subtraction")
    print ("3) Multiplication")
    print ("4) Division")
    print ("5) Quit calculator.py")
    print (" ")
    choice = int(input("Choose your option: "))
    if choice == 1:
        add1 = int(input("Add this: "))
        add2 = int(input("to this: "))
        print (add1, "+", add2, "=", add1 + add2)
    elif choice == 2:
        sub2 = int(input("Subtract this: "))
        sub1 = int(input("from this: "))
        print (sub1, "-", sub2, "=", sub1 - sub2)
    elif choice == 3:
        mul1 = int(input("Multiply this: "))
        mul2 = int(input("with this: "))
        print (mul1, "*", mul2, "=", mul1 * mul2)
    elif choice == 4:
        div1 = int(input("Divide this: "))
        div2 = int(input("by this: "))
        print (div1, "/", div2, "=", div1 / div2)
    elif choice == 5:
        loop = 0
        print ("Thankyou for using calculator.py!")