Wrong results for calculator subtraction and division

问题

My addition and multiplication work just fine. However, for subtraction, if I input 2 numbers, 3 and 1, the answer would be -2, which is obviously incorrect. Division is also not functioning properly.

I can input 2 numbers, 8 and 4, and it would tell me the answer is 0.5, which is also incorrect.

What went wrong in my code?

print("Welcome to Calculator!")

class Calculator:
    def addition(self,x,y):
        added = x + y
        return added
    def subtraction(self,x,y):
        subtracted = x - y
        return subtracted
    def multiplication(self,x,y):
        multiplied = x * y
        return multiplied
    def division(self,x,y):
        divided = x / y
        return divided

calculator = Calculator()

print("1 \tAddition")
print("2 \tSubtraction")
print("3 \tMultiplication")
print("4 \tDivision")
operations = int(input("What operation would you like to use?:  "))

x = int(input("How many numbers would you like to use?:  "))

if operations == 1:
    a = 0
    sum = 0
    while a < x:
        number = int(input("Please enter number here:  "))
        a += 1
        sum = calculator.addition(number,sum)
    print("The answer is", sum)
if operations == 2:
    s = 0
    diff = 0
    while s < x:
        number = int(input("Please enter number here:  "))
        s += 1
        diff = calculator.subtraction(number,diff)
    print("The answer is", diff)
if operations == 3:
    m = 0
    prod = 1
    while m < x:
        number = int(input("Please enter number here:  "))
        m += 1
        prod = calculator.multiplication(number, prod)
    print("The answer is", prod)
if operations == 4:
    d = 0
    quo = 1
    while d < x:
        number = int(input("Please enter number here:  "))
        d += 1
        quo = calculator.division(number, quo)
    print("The answer is", quo)

回答1:

if operations == 4:
    d = 0
    quo = 1
    while d < x:
        number = int(input("Please enter number here:  "))
        d += 1
        quo = calculator.division(number, quo)
    print("The answer is", quo)

The first time through quo becomes 8. Then it goes through again with 4 as number and 8 as quo. 4 / 8 = .5

Here's an alternative solution using reduce from the functools library.

if operations == 4:
    quo = 1
    numbers = list()
    while len(numbers) < x:
        number = int(input("Please enter number here:  "))
        numbers.append(number)
    quo = reduce(calculator.division, numbers)
    print("The answer is", quo)

I'd like to know why this was downvoted when it is indeed the answer why division wasn't working...

回答2:

Issue is with these lines..

diff = 0
while s < x:
   number = int(input("Please enter number here:  "))
   s += 1
   diff = calculator.subtraction(number,diff)
print("The answer is", diff)

Lets say input is 2 line number 3 of the above snippet, The difference in the first iteration of the loop, number (input) is 2 and diff is already 0

2-0 = 2 diff becomes 2 now Input is 1 in the second iteration,
1 -2 = -1 number is 1 and 1 - diff will become diff. that is -1.

Since in the loop you mentioned, (number,diff) - subtraction happens in the same order

来源：https://stackoverflow.com/questions/45383183/wrong-results-for-calculator-subtraction-and-division

标签

python

python-3.x

calculator