这个循环将如何结束

Question

Opening Again Edit : How to end this one

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
    vector<string> s;
    string word;

    while(cin >> word)
        {
            s.push_back(word);
        }



        for(auto i =0; i < s.size(); i++)
        {
            for(auto &c : s[i])
            c = toupper(c);
        }

        int j=1;
        for(auto c : s)
        {
              cout << c << " ";
              if(j%8==0)
              {
                  cout << "\n";
              }
              j++;
        }  
}

1. Other method can be used like putting word != "end" or something like that in while loop but it will create and extra word which i dont want.

2. I am not getting a thing why when i give space between two words like, Hello my name is james(in input) then why c++ treats it like different string and strors in different blocks of vector. I am new at c++ programming as you can see, but a old C programmer, not very old 3 month older, college guy.

---

This is an example from book c++ primer 5th edition. My question how this while loop will end I tried everything like enter, entering 0 there a many examples in this book like this.

int main()
{
      vector<unsigned> scores(11, 0);          
      unsigned grade;
      while (cin >> grade)
      { 
            if (grade <= 100) // handle only valid grades
            ++scores[grade/10];
      }

      for(auto c : scores)
      {
           cout << c << endl;
      }
}

Answer 1

The expression cin >> grade yields false (when evaluated as boolean) if the input operation failed. This happens if you reach the end of the input (EOF) or if the itput could not be parsed as the according type. Since whitespace is skipped, hitting enter doesn't exit the loop. Since a zero is a valid unsigned number, that doesn't trigger loop exit either. Entering a letter would do the job, or the (OS-specific) key combo to signal EOF.

Answer 2

The expression (cin >> end) has a return value: the object cin . This is what allows you to do stuff like cin >> x >> y . The reason the loop ends is that the boolean (truth) value of the object cin is equal to the status of the input (probably your terminal) that it is reading from. If it reaches the end of input, cin will be evaluated as false and the loop ends.

As the commenters have said, you can use Ctrl-D or Ctrl-Z in a terminal to cause cin to read the "End of File" marker.