整数到罗马数字，不能使用 def。 功能

Question

I have a homewrok assignment to convert a roman numeral to an integer. I am stuck at the part of the actual "formula" to change the roman numerals to integers and subtract/add them to the next one. We have not learned the "def" function yet so I cannot use that. Here is the code I have so far. I am just three weeks into coding so it is probably not very good..

DictOfRomanNumerals = {"I":1, "II":2, "III":3, "IV":4, "V":5, "IX":9, "X":10,
                       "XL":40, "L":50, "XC":90, "C":100, "CD":400, "D":500,
                       "CM":900, "M":1000}

UserInput = input("Type in a Roman Numeral")

i=0
ouput=0

for i in range(0, len(UserInput)):
    i = i + 1

    if len(UserInput) == 1:
        print((DictOfRomanNumerals[UserInput[0]]))
    else:
        if len(UserInput) > 1: 

Answer 1

To solve this, create some possible numerals and their values and some special values like 4, 9, 40, 90, 400, 900. Now scan the given string, if some substring is present in the table, then take its value into result, then check for the next, for next match, it adds the value with the result, finally forms the number.

roman = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000,'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}
          s = input("Type in a Roman Numeral")
          i = 0
          num = 0
          while i < len(s):
             if i+1<len(s) and s[i:i+2] in roman:
                num+=roman[s[i:i+2]]
                i+=2
             else:
                #print(i)
                num+=roman[s[i]]
                i+=1
          print(num)