Conversion from Roman Number to Decimal

Conversion from roman number to decimal is quite straightforward if you look at the pattern of the number. You can start from the rightmost letter of roman number and keep on adding the decimal number that it corresponds to. But when the letter encountered while moving left is smaller than the maximum value of the letter encountered previously we need to subtract it. For example take XLV, rightmost letter is V which is 5 , the second one is L which is 50 and the third one is X which is 10 (this is less than the max value encountered, 50, so we need to subtract it. Thus the total is 5+50-10 = 45.

  
/*I - 1
V - 5
X -10
L - 50
C - 100
D -500*/

int get_val(char roman) {

 switch (roman) {
  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;
  default:
   return 0;
 }
 return 0;
}

int roman_to_int (const std::string &roman) {
 int max = 0;
 int num = 0;
 int len = roman.length() - 1;
 while(len >= 0) {
  int val = get_val(roman[len]);

  if(val < max)
   num -= val;
  else {
   num += val;
   max = val;
  }
  len--;
 }
 return num;
}