//Changing Roman Numerals to Decimal notation project

#include<iostream>
#include<string>
#include<cmath>
#include<cstdlib>
using namespace std;

int apply(int n1, char op, int n2);
int romanToDec(string rn);
bool isRomanDigit(char rd);
bool GTE(char rd1, char rd2);
string decToRoman(int dec);

const string RDIGITS = "IVXLCDM";

int main(){
  string rn1, rn2;
  int n1, n2, result;
  char op;

  //prompt and read roman numeral
  cout << "Enter an expression with roman numerals: ";
  cin >> rn1 >> op >> rn2;
 
  while(cin){
    n1 = romanToDec(rn1);
    n2 = romanToDec(rn2);
    result = apply(n1, op, n2);
    cout << rn1 << " (" << n1 << ") " << op << " " 
	 << rn2 << " (" << n2 << ") = " << decToRoman(result)
	 << " (" << result << ")" << endl;

    //prompt and read roman numeral
    cout << "Enter an expression with roman numerals: ";
    cin >> rn1 >> op >> rn2;
  }  

  cout << endl << "Exiting.." << endl;
}


//romanToDec()----------------------------------------------------------
int romanToDec(string rn){
  int i = 0, sum = 0;

  while((i < rn.length()) && (isRomanDigit(rn[i])) && (GTE(rn[i], rn[i+1]))){
  if(rn[i] == 'I')
    sum += 1;
  else if (rn[i] == 'V')
    sum += 5;
  else if (rn[i] == 'X')
    sum += 10;
  else if (rn[i] == 'L')
    sum += 50;
  else if (rn[i] == 'C')
    sum += 100;
  else if (rn[i] == 'D')
    sum += 500;
  else if (rn[i] == 'M')
    sum += 1000;

  ++i;
  }

  return sum;
}

//isRomanDigit()---------------------------------------------------------
bool isRomanDigit(char rd){
  if((rd == 'I') || (rd == 'V') || (rd == 'X') || (rd == 'L') || (rd == 'C') || (rd == 'D') || (rd == 'M'))
    return true;
  else {
    cerr << "Error -- unknown digit: " << rd << endl;
    return false;
  }

}

/* GTE() ------------------------------------------------------
 * >= for Roman Digits
 * returns true if rd1 >= rd2
 * used to verify additive notation for Roman Numbers
 */

bool GTE(char rd1, char rd2){
  int i, j;
  i = RDIGITS.find(rd1, 0);
  j = RDIGITS.find(rd2, 0);
  if(i >= j)
    return true;
  else{
    cerr << "***ERROR*** not additive notation: " << rd1 << rd2 << endl;
    return false;
  }
}

// apply()--------------------------------------------------------
int apply(int n1, char op, int n2){
  if(op == '+')
    return n1 + n2;
  else if(op == '-')
    return n1 - n2;
  else if(op == '^')  
    return (int)pow((double)n1, (double)n2);
  else if(op == '/')
    return n1 / n2;
  else if(op == '*')
    return n1 * n2;
  else if(op == '%')
    return n1 % n2;
  else{
    cerr << "Error -- illegal operator: " << op << endl;
    exit(0);
  }
}


/* decToRoman() ------------------------------------------------
 * for decimals to roman
 */

string decToRoman(int dec){
  string result = "";
  int remainingDecimalNumber = dec;

  while(remainingDecimalNumber >= 1000){
    remainingDecimalNumber -= 1000;
    result += "M";
}
  while(remainingDecimalNumber >= 500){
    remainingDecimalNumber -= 500;
    result += "D";
}
  while(remainingDecimalNumber >= 100){
    remainingDecimalNumber -= 100;
    result += "C";
  }
  while(remainingDecimalNumber >= 50){
    remainingDecimalNumber -= 50;
    result += "L";
  }
  while(remainingDecimalNumber >= 10){
    remainingDecimalNumber -= 10;
    result += "X";
  }
  while(remainingDecimalNumber >= 5){
    remainingDecimalNumber -= 5;
    result += "V";
  }
  while(remainingDecimalNumber >= 1){
    remainingDecimalNumber -= 1;
    result += "I";
  }
  return result;
}//Changing Roman Numerals to Decimal notation project