关于利用calss String来实现统计键盘输入的英文单词中元音字母，但有点问题，请大家帮忙！

具体代码为：  
#include  <iostream.h>  
 
class  String;  
istream&  operator>>(istream&,String&);  
ostream&  operator<<(ostream&,String&);  
 
class  String      
{  
public:  
           String();  
           String(const  char*);  
           String(const  String&);  
 
           virtual  ~String();  
 
           String&  operator=(const  String&);  
           String&  operator=(const  char*);  
 
           bool  operator==(const  String&);  
           bool  operator==(const  char*);  
             
           char&  operator[](int);  
 
           int  size()  {  return  _size;}  
           char*  c_str()  {return  _string;}  
 
private:  
           int  _size;  
           char  *_string;  
 
           void  init(const  char*);  
           void  init(const  String&);  
 
 
};  
////////////////////////////////////////////////////////////////  
 
#include  "String.h"  
#include  <string.h>  
#include  <assert.h>  
#include  <iomanip.h>  
//////////////////////////////////////////////////////////////////////  
//  Construction/Destruction  
//////////////////////////////////////////////////////////////////////  
 
inline  void  
String::init(const  char  *s)  
{  
           if(!s)  
           {  
                       _size=0;  
                       _string=0;  
           }  
           else  
           {  
                       _size  =  strlen(s);  
                       _string  =  new  char[_size+1];  
                       strcpy(_string,s);  
           }  
}  
 
inline  void  
String::init(const  String  &rhs)  
{  
           _size=rhs._size;  
           if(!rhs._string)  
                       _string=0;  
           else  
           {  
                       _string  =  new  char[_size+1];  
                       strcpy(_string,rhs._string);  
           }  
}  
 
String::String()  
{  
           init(0);  
}  
 
String::String(const  char  *s)  
{  
           init(s);  
}  
 
String::String(const  String  &rhs)  
{  
           init(rhs);  
}  
 
bool  String::operator  ==(const  String  &rhs)  
{  
           if(_size  !=  rhs._size)  
                       return  false;  
           return  strcmp(_string,rhs._string)?false:true;  
}  
 
bool  String::operator==(const  char  *s)  
{  
           return  strcmp(_string,s)?false:true;  
}  
 
char&  String::operator  []  (int  elem)  
{  
           assert(elem  >=  0  &&  elem  <  _size);  
           return  _string[elem];  
}  
 
String&  
String::operator  =  (const  char  *s)  
{  
           if(!s)  
           {  
                       _size=0;  
                       delete  []  _string;  
                       _string=0;  
           }  
           else  
           {  
                       _size=strlen(s);  
                       delete  []  _string;  
                       _string  =  new  char[_size+1];  
                       strcpy(_string,s);  
           }  
           return  *this;  
}  
 
String&  
String::operator  =  (const  String  &rhs)  
{  
           if(this  !=  &rhs)  
           {  
                       delete  []  _string;  
                       _size=rhs._size;  
 
                       if(!rhs._string)  
                                   _string=0;  
                       else  
                       {  
                                   _string  =  new  char[_size+1];  
                                   strcpy(_string,rhs._string);  
                       }  
           }  
           return  *this;  
}  
 
istream&  operator>>(istream  &io,String  &s)  
{  
           const  int  limit_string_size  =  4096;  
           char  inBuf[limit_string_size];  
 
           io  >>  setw(limit_string_size)  >>  inBuf;  
             
           s  =  inBuf;  
           return  io;  
}  
 
ostream&  operator<<(ostream&  os,String  &s)  
{  
           return  os  <<  s.c_str();  
}  
 
String::~String()  
{  
           delete  []  _string;  
}  
 
主函数：  
#include  "String.h"  
 
int  main()  
{  
           int  aCnt=0,iCnt=0,eCnt=0,oCnt=0,uCnt=0,bCnt=0,dCnt=0,fCnt=0,sCnt=0,  
                       tCnt=0,theCnt=0,itCnt=0,wdCnt=0,notVowel=0;  
 
             String  buf,the("the"),it("it");  
 
           while(cin  >>  buf)  
           {  
                       ++wdCnt;  
                       cout<<buf<<'  ';  
                       if(wdCnt  %  12==0)  
                                   cout<<endl;  
 
                       if(buf==the  &brvbar;  &brvbar;buf=="The")  
                                   ++theCnt;  
 
                       else  if(buf==it  &brvbar;  &brvbar;buf=="It")  
                                   ++itCnt;  
 
                       for(int  ix=0;  ix<buf.size();  ++ix)  
                       {  
                                   switch(buf[ix])  
                                   {  
                                               case  'a':  case'A':  ++aCnt;  break;  
                                               case  'e':  case'E':  ++eCnt;  break;  
                                               case  'i':  case'I':  ++iCnt;  break;  
                                               case  'o':  case'O':  ++oCnt;  break;  
                                               case  'u':  case'U':  ++uCnt;  break;  
                                               default:  ++notVowel;  break;  
                                   }  
                       }  
           }  
 
           cout<<"\n\n";  
           cout<<"Words  read:"<<wdCnt<<"\n\n"  
                       <<"the/The:"<<theCnt<<"\n"  
                       <<"it/It:"<<itCnt<<"\n\n"  
                       <<"non-vowels  word:"<<notVowel<<"\n\n"  
                       <<"a:"<<aCnt<<"\n"  
                       <<"e:"<<eCnt<<"\n"  
                       <<"i:"<<iCnt<<"\n"  
                       <<"o:"<<oCnt<<"\n"  
                       <<"u:"<<uCntendl;  
           return  0;  
}  
问题所在：在主函数中的while循环怎么也退不出来，不知道什么原因？请各位高手多多指点！谢谢！