十六進制字符串轉十六進制數

static int tolow(int c)
{
    if (c >= 'A' && c <= 'Z')
    {
        return c + 'a' - 'A';
    }
    else
    {
        return c; 
    }
}
static int htoi(char s[])
{  
    int i;
    int n = 0;
    if (s[0] == '0' && (s[1]=='x' || s[1]=='X'))
    {
        i = 2;
    }
    else
    {
        i = 0;
    }
    for (; (s[i] >= '0' && s[i] <= '9') || (s[i] >= 'a' && s[i] <= 'z') || (s[i] >='A' && s[i] <= 'Z');++i)
    {
        if (tolow(s[i]) > '9')
        {
            n = 16 * n + (10 + tolow(s[i]) - 'a');
        }
        else
        {
            n = 16 * n + (tolow(s[i]) - '0');
        }
    }
    return n;
}

將十六進制字符串轉換成可用十六進制表示的數字