compare strings

string bigger(string a, string b)
{
    if(a == b) return a;
    if(a.length() != b.length())
        return ((a.length() > b.length()) ? (a) : (b));
    int i = 0;
    while(a[i] == b[i])
        i++;
    return ((a[i] > b[i]) ? (a) : (b));
}

bool compare(string a, string comp, string b)
{
    if(comp == "==" || comp == ">=" || comp == "<=")
        if(a == b) return true;
    if(comp == "==") return false;
    if(comp == "!=") return true;
    string bigger_num = bigger(a, b);
    if((comp == ">" || comp == ">=") && bigger_num == a) return true;
    if((comp == "<" || comp == "<=") && bigger_num == b) return true;
    return false;
}