Roman Numeral converter assistance

[popup271]

I have to write a program to convert roman numerals into actual numbers. Like I to 1 or XI to 11. I have to read the roman numerals from a file which is also easy, but my question is how do i convert a string worth at a time.

This is what i have to read them him and it works, but after i fin rm1(roman numeral one) in a string form how would I go about converting the string.

All help or ideas would be helpful. :) Thanks

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

void get_Data(ifstream& fin, string& rm1, string& rm2, char& op)
{
	fin >> rm1 >> rm2 >> op;
}

int convert_roman_to_number(char x)
{

}


void main()
{
	ifstream fin;
	string rm1 = "", rm2 = "";
	char op = ' ';

	fin.open("MP4.txt");

	get_Data(fin, rm1, rm2, op);
	


	system("pause");
}

Input File contents: (no enter before everything)

MCCXXVI CV +
MCCXXCI MCCXXI /
V I -
DL DXXXXVIII -
D L /
MDI CXI +
XXV IIII /
XI CII *

[ritstudent]

The method I would suggest is using an if/else if structure that would recursively parse the string. I will reply back with a solution soon.

Your base case is an empty string.
Here are some tips:
http://blog.functionalfun.net/2009/01/project-euler-89-converting-to-and-from.html

[popup271]

Need help please!

[Keppit]

If you're going to read in the roman numerals as complete strings, you could use the .at() function to analyze each individual character.

I'd make a separate int var and add a certain amount depending on which letter it is.
I'd use a for loop. Maybe something like this:

int d1 = 0, d2 = 0; //"d" standing for decimal

for (int = 0; i < rm1; i++)
{	
	switch (rm1.at(i))
	{
		case 'I': d1 += 1; break;
		case 'V': d1 += 5; break;
		case 'X': d1 += 10; break;
		case 'L': d1 += 50; break;
		case 'C': d1 += 100; break;
		case 'D': d1 += 500; break;	
		case 'M': d1 += 1000; break;
	}
}
//and then do the same for the second string 

[Keppit]

This solution of course doesn't account for stuff like the roman numeral IV, but it doesn't look like there's anything like that in your input file.

[popup271]

New Problem........
When i run i get a
R6010 abort code.....
Looked it up and people are saying it is trying to read a file that is not there
but no one cares to say how to fix it

[ShodanHo]

#include <iostream>
#include <list>
#include <fstream>
using namespace std;

// stream a pair
template<typename A, typename B>
ostream & operator<<(ostream& os, const pair<A,B>& p)
{
  os << '(' << p.first << ',' << p.second << ')';
  return os;
}

// stream a list
template<typename T>
ostream & operator<<(ostream& os, const list<T>& l)
{
  for (auto it = l.cbegin(); it != l.cend(); ++it) {
    os << *it;
  }
  return os;
}

// convert a roman token to a number. return 0 if invalid
static unsigned RomanTokenToDecimal(char c)
{
  switch (c) {
  case 'I': return 1;
  case 'V': return 5;
  case 'X': return 10;
  case 'L': return 50;
  case 'C': return 100;
  case 'D': return 500;
  case 'M': return 1000;
  }
  return 0;
}

/*
 * convert a string of Roman symbols to an unsigned number.
 * no checks are done on correctness of input
 * IV => 4
 * IVX => 4
 * VV => 10
 */
static unsigned RomanStringToNumber(const string& str)
{
  /* step 1: convert each token to a sign and a number
   * step 2: work out if there is subtraction of the number to take place
   * step 3: then calculate the number
   *
   * eg: MCMLIX:
   * step 1:
   * M: + 1000
   * C: + 100
   * M: + 1000
   * L: + 50
   * I: + 1
   * X: + 10
   * 
   * step 2:
   * M: + 1000
   * C: - 100 <--- subtract because next number is greater
   * M: + 1000
   * L: + 50
   * I: - 1 <--- subtract because next number is greater
   * X: + 10
   *
   * step3: +1000-100+1000+50-1+10=1990
   */
  list< pair<bool,unsigned> > sign_value; // true(+),false(-)
  // step 1
  for (auto &c: str) {
    sign_value.push_back( pair<bool,unsigned>(true, RomanTokenToDecimal(c)) );
  }

  // step 2: change the sign if the subsequent value is higher
  for (auto it = sign_value.begin(); it != sign_value.end(); ++it) {
    if (it != sign_value.begin()) {
      auto prev = it; --prev;
      if (prev->second < it->second) // do we need to subtract
	prev->first = false;
    }
  }

  // step 3: sum the numbers
  unsigned sum = 0;
  for (auto it = sign_value.cbegin(); it != sign_value.cend(); ++it) {
    sum = sum + (it->first ? it->second : -it->second);
  }

  //cout << sign_value << ' ' << sum << endl;
  return sum;
}

/*
 * not sure if romans had negative numbers, but allow negative numbers
 */
static int doOperation(unsigned arg1, unsigned arg2, char op)
{
  switch (op) {
  case '+': return arg1 + arg2;
  case '-': return arg1 - arg2;
  case '*': return arg1 * arg2;
  case '/': return arg1 / arg2;
  }
  return 0;
}

int main()
{
  // do a little bit of checking
  {
    string a("I");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("II");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("III");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("IV");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("V");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("VI");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("VII");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("VIII");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("IX");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("X");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }
  {
    string a("MCMXL");
    cout << a << ':' << RomanStringToNumber(a) << endl;
  }

  // open the file
  ifstream fin;
  fin.open("MP4.txt");

  // read line by line, performing the operation
  for (;;) {
    string rm1, rm2;
    char op;
    fin >> rm1 >> rm2 >> op;
    if (fin.fail()) break;

    cout << "rm1=" << rm1 << " rm2=" << rm2 << " op=" << op << " ";

    cout << RomanStringToNumber(rm1) << op
	 << RomanStringToNumber(rm2) << "="
	 << doOperation(RomanStringToNumber(rm1),
			RomanStringToNumber(rm2),op) << endl;
  }
  fin.close();
  return 0;
}

I:1
II:2
III:3
IV:4
V:5
VI:6
VII:7
VIII:8
IX:9
X:10
MCMXL:1940
rm1=MCCXXVI rm2=CV op=+ 1226+105=1331
rm1=MCCXXCI rm2=MCCXXI op=/ 1301/1221=1
rm1=V rm2=I op=- 5-1=4
rm1=DL rm2=DXXXXVIII op=- 550-548=2
rm1=D rm2=L op=/ 500/50=10
rm1=MDI rm2=CXI op=+ 1501+111=1612
rm1=XXV rm2=IIII op=/ 25/4=6
rm1=XI rm2=CII op=* 11*102=1122

[ritstudent]

With recursion:

This code may be executed on the commandline with ./main XVII for instance.

#include <iostream>

using namespace std;
int getDecVal( char );
string tail( string const&, size_t const );
int rome_to_dec( string );

int main( int argc, char** argv ){
	cout << rome_to_dec( argv[1] );
	return 0;
}

int rome_to_dec( string str ){
	int mulVal;
	if( str.size() == 0 ){
		return 0;
	}else{
		mulVal = getDecVal(str[0]);
		if( str.length() > 1 ){
			if( mulVal < getDecVal(str[1]) ){
				mulVal = -mulVal;
			}
		}
		return mulVal + rome_to_dec( tail(str, str.size()-1) );
	}	
}

string tail( string const& source, size_t const length){
	if( length >= source.size() ){ return source; }
	return source.substr(source.size() - length);
}

int getDecVal( char x ){
	switch(x){
	case 'I': return 1;
	case 'V': return 5;
	case 'X': return 10;
	case 'L': return 50;
	case 'C': return 100;
	case 'D': return 500;
	case 'M': return 1000;
	}
	return 0; // Continue the statement
	
}

However, this solution that I provided does not account for invalid user input. For instance, XIIV is not valid. However this algorithm that I presented will return the number 15. You would need to add another function that is verifying that the user input is valid--or build that into the recursion (which I highly discourage).

I checked my solutions against this:
http://westerlund09.wikis.birmingham.k12.mi.us/file/view/roman_numerals.jpg