C function that takes a string with the valid roman numerals (IVXLCDM) and return the integer that those numerals represent

roman_to_int.c

int romanToInt(char *s){
    int i;
    int num;
    num = 0;
    i = 0;
    while(s[i] != '\0')
    {
        if(s[i] == 'I')
        {
            if(s[i + 1] == 'V')
            {
                num += 4;
                i += 2;
            }
            else if(s[i + 1] == 'X')
            {
                num += 9;
                i += 2;
            }
            else
            {
                num += 1;
                i++;
            }
        }
        else if(s[i] == 'X')
        {
            if(s[i + 1] == 'L')
            {
                num += 40;
                i += 2;
            }
            else if(s[i + 1] == 'C')
            {
                num += 90;
                i += 2;
            }
            else
            {
                num += 10;
                i++;
            }
        }
        else if(s[i] == 'C')
        {
            if(s[i + 1] == 'D')
            {
                num += 400;
                i += 2;
            }
            else if(s[i + 1] == 'M')
            {
                num += 900;
                i += 2;
            }
            else
            {
                num += 100;
                i++;
            }
        }
        else if(s[i] == 'D')
        {
            num += 500;
            i++;
        }
        else if(s[i] == 'M')
        {
            num += 1000;
            i++;
        }
        else if(s[i] == 'L')
        {
            num += 50;
            i++;
        }
        else if(s[i] == 'V')
        {
            num += 5;
            i++;
        }
           
    }
    return(num);
}