Read strings from the standard input, concatenating what is read into one large string

Question

For some reason i cannot get for loop to work. It doesn't print anything. Here is code:

#include <iostream>
#include <string>

using std::string;
using std::cin;
using std::cout;
using std::endl;

int main()
{
    string concatenated;
    for (string buffer; cin >> buffer; concatenated += buffer);
    cout << "The concatenated string is " << concatenated << endl;

    return 0;
}

I can't reproduce. Do you actually input something and press enter? — HolyBlackCat, Apr 10 '18 at 10:48
Sorry I misspelled, it compiles. But after running it doesn't print anything. — Boban Ljubicic, Apr 10 '18 at 10:50
you have ';' at the end of the for loop. your should remove it and will work fine — Arkady Godlin, Apr 10 '18 at 10:51
@Sniper2Wolf It is working fin. [See here working](https://ideone.com/Fh7d2Z) — cse, Apr 10 '18 at 10:56
But perhaps it would be better form to actually have an empty block `{}` after the `for(...)` to telegraph what's going on? — Andrew Jaffe, Apr 10 '18 at 10:56
I am working through the book c++ primer, and I need to do exercise which says "Write a program to read strings from the standard input, concatenating what is read into one large string. Print the concatenated string." — Boban Ljubicic, Apr 10 '18 at 10:57
i think you should add an exit string code, to break from the for loop. on visual studio 2015 except CTRL+C i was not able to exit this loop, and this keys throw exception. — Arkady Godlin, Apr 10 '18 at 11:01
@ArkadyGodlin Ok I have found the problem, I just needed to press CTRL+Z to exit the for loop. — Boban Ljubicic, Apr 10 '18 at 11:03
@Sniper2Wolf it is not a full solution you should add then try catch for your code or add an exit string so you can break from the loop for example if (buffer == "exit") break; — Arkady Godlin, Apr 10 '18 at 11:11

cse · Accepted Answer · 2018-04-10T11:25:25.897

The problem is that for-loop will not exit automatically. It is continually go in loop and wait for next input. That's why you are not getting any outpur at your end.

You should enter Control+Z on Windows and Control+D on Unix plateforms to enter EOF character on . See this to know more.

The code is fine. See it working here

Following is output from my local. The code used is same as posted and available here.

score 0 · Answer 2 · answered Apr 10 '18 at 11:18

You need something to stop the loop from waiting for more input.. You may use a special string to do this..

#include <iostream>
#include <string>

using std::string;
using std::cin;
using std::cout;
using std::endl;

int main()
{
    string concatenated;
    for (string buffer; cin >> buffer && buffer!="STOP"; concatenated += buffer);
    cout << "The concatenated string is " << concatenated << endl;

    return 0;
}

Read strings from the standard input, concatenating what is read into one large string

2 Answers2