关于缓冲 关于^z的小小疑问

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main()
{
    string currWord,preWord;
    cout<<"Enter somewords:(Ctral+Z to end)"<<endl;
    while(cin>>currWord)
    {
#ifndef NDEBUG
        cout<<currWord<<endl;
#endif
        if(!isupper(currWord[0]))
            continue;
        if(currWord==preWord)
            break;
        else
            preWord=currWord;
    }
    if(currWord==preWord&&!currWord.empty())
        cout<<"The is no repeated wor that has initial capital."<<endl;
    else
        cout<<"There is no repeated word that has initial capital."<<endl;

    return 0;
}