这个代码麻烦帮我看一下哪里错，谢谢了，，，，是要输出不是标点符号的字符

# include <iostream>
# include <cctype>
# include <string>
using namespace std;
void main()
{
    string s1;
    cin >> s1;
    for(string::size_type index=0,inde_x=0;index<s1.size();++index)
    {
        if(!ispunct(s1[index]))
            s2[++inde_x]=s1[index];
    }
}