新手求助

//虽然用了STL，但用纯C语言也不会麻烦多少
#include <string>
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
     using namespace std;
     unsigned i, n;
     string str;
     string::iterator siter;
     vector<char> vchar;
     vector<char>::iterator viter;
     cin >> str;
     for (siter=str.begin();siter!=str.end();++siter)
         if (find(vchar.begin(),vchar.end(),*siter)==vchar.end())
             vchar.push_back(*siter);
     for (viter=vchar.begin();viter!=vchar.end();++viter)
     {
         i=n=0;
         while ((i=str.find_first_of(*viter,i))!=string::npos)
         {n++;i++;}
         cout << "字符" << *viter << "出现了" << n << "次" << endl;
     }
     return 0;
}

//修改了一下，不再预先搜索出现的字母，而采用直接删除的方式
#include <string>
#include <iostream>
int main()
{
     using namespace std;
     unsigned n;
     char c;
     string str;
     string::iterator siter;
     cin >> str;
     while (str.length())
     {
         c=*str.begin(); //str[0]
         for (n=1, siter=str.erase(str.begin());siter!=str.end();)
             if (c==*siter)
             {
                 n++;
                 siter=str.erase(siter);
             }
             else
                 siter++;
         cout << "字符" << c << "出现了" << n << "次" << endl;
     }
     return 0;
}


//纯C语言版
#include <stdio.h>
int main()
{
     char str[64], *phead=str, *pnow, c;
     unsigned n;
     gets(str);
     while (*phead!=0)
     {
         for (n=1, c=*phead, pnow=phead+1;*pnow;pnow++)
             if (c==*pnow)
             {
                 n++;
                 *pnow=-1;   //用-1标明此处已被删除
             }
         printf("字符%c出现了%d次\n",c,n);
         while (*++phead==-1);
     }
    return 0;
}