如何解决浮点计算问题？

Question

So, last week, I got some work sent to me for Python 3, and one of the questions goes as follows: "Write (a) program which inputs the year. Your program should output whether it is a leap year or not. To work out if it is a leap year, test whether it is exactly divisible by 4."

This is what I've got so far:

yearStr = input("Please input a year: ")
year = float(yearStr)

calculation = year / 4

print(calculation)

if calculation == .0:
    print("This is a leap year.")
else:
    print("This is not a leap year.")

When I run the program, the IF statement doesn't work as intended. Could you help me, please?

Answer 1

Division does not yield zero if the number is evenly divisible, so this method cannot work.

Rather, use the modulo ( % ) operator to get the remainder of the division:

year = int(yearStr)
calculation = year % 4
if calculation == 0: # leap year
    ...

And note that strictly speaking, leap year determination is a bit more complex than just being divisible by four. But it'll do for the next 79 years.

Answer 2

Your problem is the performance of the code. To check if the year is leap, you have to put different conditions. You can now use this code:

year = int(input("Please input a year: "))

if ((year%400 == 0) or ((year%4 == 0) and (year%100 != 0))):
    print("This is a leap year.")
else:
    print("This is not a leap year.")

Answer 3

You are comparing calculation with 0, which is true only if the year was 0. You can check if integer value is equal to number itself.

calculation = year / 4

print(calculation)

if int(calculation) == calculation:
    print("This is a leap year.")
else:
    print("This is not a leap year.")

Still, this is not a good way to solve this problem, there is a remainder operation - %. For example 5 % 2 = 1 . You can use it this way:

yearStr = input("Please input a year: ")
year = float(yearStr)

print(calculation)

if calculation % 4 == 0:
    print("This is a leap year.")
else:
    print("This is not a leap year.")