为什么Loop永不结束？

Question

So I feel that I am close to solving a programming assignment that takes the most used word of each line and prints it on a line. So for example:

I am a man, am right?
I don't know if i like that.
It's okay to not feel okay.

Would print: "am i okay" (punctuations and case are ignored for the assignment)

This is what I have done so far, but the problem is that the while loop that scans the lines never terminates and thus never prints the output in the external for loop. Anybody see where I went wrong?

string line;
vector<string> result;
while(getline(cin,line)){     //on each line

}

Answer 1

Your loop is correct as written; you just don't know how to signify the end of input. You're sitting there waiting for the program to progress, but the program is sitting there waiting for you to give it more input.

Press Ctrl+D (Linux) or Ctrl+Z (Windows) to send the EOF character/signal/potion to end the loop.

This way, all the common shell techniques like file redirection and pipes will also work.

Introducing artificial means like a double-newline or some magic command is non-conventional and makes your program harder to automate. (And making your program magically know that one of the newlines came from a keyboard hit rather than copy/pasting, is just not possible. Nor do you want it to be! That breaks a ton of valuable abstractions.) When writing a command-line tool, stick to standard practices as much as possible.

Answer 2

Currently your program is waiting for an EOF character which indicates the input has ended. If you are running this and entering the input from the command line, you can manually insert an EOF by pressing Ctrl+D on *nix, or Ctrl+Z on windows. This will cause your program to break out of your getline loop.

If you would rather not do that, you need a way to break out of the getline loop, otherwise it will continue to run in that loop.

A nice idea might be detecting an empty line, so pressing enter twice ends the loop:

while(getline(cin,line)){     //on each line
    if(line == "")
        break;
    ...
}