Roman to Integer

int a[200];

int romanToInt(char* s) {
int num = 0;
a[0] = 0;
a['I'] = 1;
a['X'] = 10;
a['C'] = 100;
a['M'] = 1000;
a['V'] = 5;
a['L'] = 50;
a['D'] = 500;

for(int i = 0 ; s[i] ; i ++)
{
if(s[i] == 'I' || s[i] == 'X' || s[i] == 'C'){
if( a[s[i+1]] > a[s[i]]){
num += (a[s[i+1]]-a[s[i]]);
i++;
continue;
}
}
num += a[s[i]];
}
return num;
}