while (cin.get(x, 10).get()) encounter a empty input NO quit loop, why?

[q1670741824]

i wish give a empty input to quit while loop, but get a keep looping result. doesn't a empty loop set a fail flag when given a blank line?

char x[10];
while (cin.get(x, 10).get())
sumt(x);
cin.clear();

without a cin.clear(); i don't think a .get() can reset input available. why keep looping?

[Chervil]

You could try adding a test for a zero-length string. The function strlen() could be used, but all that is really required is to test that the first character is not the null terminator.

while (cin.getline(x, 10) && x[0])
    sumt(x);

[q1670741824]

what i wanna know is that how my code runs, the mechanism, the sequence...

[Protomega]

http://www.cplusplus.com/forum/beginner/119218/

This might help you out a little.

[q1670741824]

chervil ur way works too. but i want to know why my way cannot work.

and i really want to know here is that, when two methods connect together like cin.get(x,10).get(), if cin.get(x,10) wrong(false) and .get() right(true), the whole entity return true?

[Chervil]

The starting point here is to consider the input data itself. The logic is built upon the required behaviour given that data.

The input here is from the keyboard, the user will enter zero or more characters and then press the enter key. That means the input buffer will contain a string of characters something like this:
"abcd\n" or "123\n" or simply "\n" for a blank line.

Now we know what the data will look like, we can consider how the program should deal with it. The requirement is to loop repeatedly until the user enters a blank line.

My suggestion was to use the getline(). This reads characters from the input buffer until the delimiter (default is newline '\n') is found. The newline itself is read and discarded. If the user had input an empty line, the fail() flag is not set, as this is considered a valid input. So in my code I added a second condition, to test for an empty string.
http://www.cplusplus.com/reference/istream/istream/getline/

Now what about the original code:

while (cin.get(x, 10).get())

Here, the cin.get(x, 10) behaves in a similar manner to getline() with the important difference that it does not remove the delimiter (newline) from the input buffer. Presumably in order to handle that, a .get() is tagged on in order to follow the reading of the string with the reading of a single character.

What is the return value in this case? Well, the while() loop is checking the result of this second get(). This will return the actual character which was read (presumably the newline '\n') or if for some reason it fails, the returned value is EOF, typically represented as -1. In either case the result is considered true since both '\n' and -1 are non-zero values.
http://www.cplusplus.com/reference/istream/istream/get/
http://www.cplusplus.com/reference/cstdio/EOF/

One alternative you could try is instead of:

    char x[10];

    while (cin.get(x, 10).get())
        sumt(x);

    cin.clear();

move the second get() inside the body of the loop, like this:

    char x[10];
     
    while (cin.get(x, 10))
    {
        cin.get(); // read and discard the delimiter
        sumt(x);  
    }
    
    cin.clear();

[q1670741824]

Thank you!

so here after cin.get(x,10) be set a fail flag, the .get will too return a EOF, and because EOF is -1 most times, so the while loop recognized it as true.

here i wanna confirm that in the condition of, say, cin.get(x,5).getline(y,11).get(); the loop test will see that last one's return value and overlook the former ones'. Is it?

i thought always that , after the cin object be set a fail flag, that following input will be skipped. and here i think what i thought is not right. the following input object will still read, but only meet that failbit, and read nothing, return false, and leave the input after that failbit still in the queue.
Do I think it the way right?
so occationally, here the last .get() meet that failbit and stop reading any further with a return value EOF which is true for the while loop.