C++:how to end while(cin >>)

#include <iostream>
#include <vector>
#include <cctype>
using  namespace std;
using std::vector;
int main() {
    vector<string> Capital;
    string word;
    while(cin>>word)
    {
    Capital.push_back(word);
    }

    for(auto &a : Capital)
    for(int i=0;i<a.size();i++)
{
    toupper(a[i]);
}
    return 0;
}

And when I input enter and command + D it does not work and repeat what I had just input.enter image description here