Why does my operation of mod (%) on a 2 digit number return zero in python

Question

I've been trying to attempt some leetcode questions as a complete beginner, and a section requires me to convert/return the thousands, hundreds, tens and units place of a number.

This is the code in python.

class Solution:
    def intToRoman(self, num: int) -> str:
        list = {1 :   'I',
                4 :   'IV',
                5 :   'V',
                9 :   'IX',
                10:   'X',
                40:   'XL',
                50:   'L',
                90:   'XC',
                100:  'C',
                400:  'CD',
                500:  'D',
                900:  'CM',
                1000: 'M'}

        thousands, hundreds, tens, unit = 0,0,0,0
        string = ""
        number = int(num)
        
        #A Thousandth number
        
        if number >= 1000:
            thousands = number - (number % 1000)              # 3549 - (3549 % 1000) = 3000

            hundreds = number - thousands;                  #// 3549 - 3000 = 549
            tens = hundreds % 100                      #// 549 % 100 = 49
            hundreds = hundreds - (hundreds % 100)     #// 549 - (549 % 100) = 500

            units = tens % 10
            tens = tens - (tens % 10)                  #// 49 - (49 % 10) = 49 - 9 = 9

            thou = thousands // 1000                     # 3

            #THOUSANDS
            for i in range(thou):
                string = string + (list[1000])

            #HUNDREDS
            hund = hundreds // 100

            if hund < 4:
                string = string +(hund * list[100])
                
            elif hund == 4:
                string = string +(list[400])
                
            elif hund == 5:
                string = string +(list[500])
                
            elif hund >= 6 and hund <= 8:
                string = string +(list[500])
                hund = hund - 5
                string = string +(hund * list[100])
                
            elif hund == 9:
                string = string +(list[900])
                
            #TENS
            ten = tens // 10

            if ten < 4:
                string = string +(ten * list[10])

            elif ten == 4:
                string = string +(list[40])

            elif ten == 5:
                string = string +(list[50])

            elif ten >= 6 and ten <= 8:
                string = string +(list[50])
                ten = ten - 5
                string = string +(ten * list[10])

            elif ten == 9:
                string = string +(list[90])
                
            #UNITS
            if unit < 4:
                string = string +(unit * list[1])
                
            elif unit == 5:
                string = string +(list[5])
                
            elif unit >= 6 and unit <= 8:
                string = string +(list[5])
                unit = unit - 5
                string = string +(unit * list[1])
            elif unit == 9:
                string = string +(list[9])

            return string

Now, my problem is that the Units variable is holding zero. I can't figure out why? This exact block of code when translated to C works properly. Is there something funky about Mod in python that I'm missing?

Ex: If the input number is 3549 (Integer has to be converted into a roman numeral), the units variable holds zero. The output should be MMMDXLIX.

Since IX in the output depends on the units variable (which holds zero for some reason), the output is MMMDXL

Btw the function only works on a number >= 1000. I've not coded any further.

Please fix your indentation. Also I am confused as to whether you are using `num` or `no` — Orbital, Jun 07 '21 at 06:23
I've edited the post. Sorry for the mess, I had copy pasting between C and Python and forgot to keep track of the variables and indentation @Orbital — Daniel Chettiar, Jun 07 '21 at 06:42
Try the whole function that I've edited if you would, @leaf_yakitori — Daniel Chettiar, Jun 07 '21 at 06:43

leaf_yakitori · Accepted Answer · 2021-06-07T07:00:34.880

you have a typo in these code block:

        if number >= 1000:
            thousands = number - (number % 1000)              # 3549 - (3549 % 1000) = 3000

            hundreds = number - thousands;                  #// 3549 - 3000 = 549
            tens = hundreds % 100                      #// 549 % 100 = 49
            hundreds = hundreds - (hundreds % 100)     #// 549 - (549 % 100) = 500

            unit = tens % 10 # you input "units" here
            tens = tens - (tens % 10)                  #// 49 - (49 % 10) = 49 - 9 = 9

            thou = thousands // 1000                     # 3

result:

MMMDXLIX

BTW, this problem got a better solution.

my code:

def intToRoman(num: int) -> str:
    roman_dict_key = [1,4,5,9,10,40,50,90,100,400,500,900,1000][::-1]
    roman_dict_value = ["I","IV","V","IX","X","XL","L","XC","C","CD","D","CM","M"][::-1]
    roman_dict = dict(zip(roman_dict_key,roman_dict_value))
    ans = ""
    for digit,roman in roman_dict.items():
        while num>=digit:
            num -= digit
            ans += roman
    return ans

Of course, it was something as simple as that. I've spent too much time on this, that I ended up missing something so simple. Thanks a lot! — Daniel Chettiar, Jun 07 '21 at 06:52
@Daniel Chettiar i recommend you to use IDE to write code, such as VScode,Pycharm.The IDE will tell if you have a typo. — leaf_yakitori, Jun 07 '21 at 06:54
Consider reversing your lists in a bit more pythonic way, such as `[::-1]` — oskros, Jun 07 '21 at 06:58

Why does my operation of mod (%) on a 2 digit number return zero in python

1 Answers1