roman converter function. need help looking at my code

[genkers]

hi i have a project due in Two days where i have to read in a file that contains integers and roman numerals. i am pretty much done with it the only problem is my function for converting roman numeral isnt 100% correct, it wont correctly convert if it has an IV, IX, CM etc. i know what the problem is but not sure how to go about it. one solution i tried was when it got to an'I', i tried to use romanNumeral.at(i+1) so that it would move to the next position, so the program would check to see if there was a 'V' or an 'X' but i don't think that actually moved it to the next position. and then i thought about letting the whole for loop run and then once it finishes running i could use find() to find instances of IV etc in the original string and subtract the correct value from the new total, so if i had XIV i would subtract 2 to give me 14, but not sure if that is possible and it wouldnt work with just IV. any hint or possible solution would be really helpful. i really dont want to rewrite the whole function since its due in 12 hours.

 void romanConverter(string romanNumeral)
{
	int decimalTotal = 0;
	
	for (unsigned int i = 0; i < romanNumeral.length(); ++i)
	{

		if (romanNumeral.at(i) == 'M')
		{
			decimalTotal += 1000;
		}

		if (romanNumeral.at(i) == 'D')
		{
			decimalTotal += 500;
		}

		if (romanNumeral.at(i) == 'C')
		{
			
			
				decimalTotal += 100;
			
		}

		if (romanNumeral.at(i) == 'L')
		{
			 
			
			
				decimalTotal += 50;
			
		}

		if (romanNumeral.at(i) == 'X')
		{
			decimalTotal += 10;
			
		}

		if (romanNumeral.at(i) == 'V')
		{ 
			
			
				decimalTotal += 5;
			
		}

		if (romanNumeral.at(i) == 'I')
		{

			decimalTotal += 1;

		
		}
		
		
	}

[Duthomhas]

You've noticed the problem is with strings like IV.

What you could do is find and replace them with a string your algorithm would like better, like IIII (which is still correct Roman Numeral, so as an added bonus your algorithm behaves properly either way).

In other words:

  1. convert all strings like IV-->IIII, IX-->VIIII, XL-->XXXX, etc.
  2. sum values of each 'digit'

By the way, whenever you notice you are doing the same thing over and over, you should consider using either a loop or a lookup table.

In your case, a lookup table would be useful to convert between 'digits' and digit values. For example, given the string

  "IVXLCDM"

you can find the index of a 'digit' (for example, X is at position 2), then use that index to look up the corresponding value:

  { 1, 5, 10, 50, 100, 500, 1000 }

The value at index 2 is: 10. :O)


Two other things to consider.

  • What if I give you a string like you find at the front of books: "vii"?
  • Your function name is not clear. Are you converting to or from Roman? Or both?
    Chose a name that represents your function best, like "convertFromRoman()".

Hope this helps.