LeetCode OJ--Roman to Integer

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

class Solution {
public:
int change(char ch)
{
int num = 0;
switch(ch)
{
case 'I':
num = 1;
break;
case 'V':
num = 5;
break;
case 'X':
num = 10;
break;
case 'L':
num = 50;
break;
case 'C':
num = 100;
break;
case 'D':
num = 500;
break;
case 'M':
num = 1000;
}
return num;
}
int romanToInt(string s) {
int i = 0;
int sum = 0;
int num = 1;
for(i = 0;i<s.size()-1;i++)
{
if(change(s[i])<change(s[i+1]))
sum -= change(s[i]);
else
sum += change(s[i]);
}
sum += change(s[i]);
return sum;
}
};

int main()
{
Solution myS;
myS.romanToInt("DCXXI");
return 0;
}