C++primer习题3.10 删除string字符串的标点

#include <iostream>
#include <string>
using namespace std;
char* my_del_dot(string s)
{
        size_t len = s.size();
        char *des = new char[len+1];
        int j = 0;
        for (size_t i = 0; i != len; ++i)
        {
                if (isalpha(s[i]))
                {
           des[j++] = s[i];
                }
        }
        des[j] = '\0';
        return des;
}
int main()
{
    string s;
        cin >> s;
        cout << my_del_dot(s) << endl;
        return 0;
}