Cant cin after terminating the while loop

Question

int n;
while(cin>>n)
    cout << n; // Run by the program if received an int value
cout << "Break from loop"; // Run by the program
cin >> n; // Skipped by the program
cout << n; // Run by the program

cant accept another input after terminating the while loop using characters.

How to accept another input if the input within the loop has been terminated using non-integer/floating-point values.

Does anyone know a cleaner way than [`cin.clear(); getline(cin,dummystring);`](http://stackoverflow.com/questions/7413247/cin-clear-doesnt-reset-cin-object)? — Beta, Feb 16 '14 at 23:05
@0x499602D2: Yes, with a touch of derision for a user who can't search for "reset cin". — Beta, Feb 17 '14 at 00:14
@Beta Well, a *better* way would be to use `ignore()` to discard the characters `std::cin.ignore(std::numeric_limits::max(), '\n')` but no, there is no "cleaner" way to do it. You *could* put the cleanup inside a function, however. — David G, Feb 17 '14 at 00:22

score 0 · Answer 1 · answered Feb 16 '14 at 23:15

int n;
while(cin>>n) // Keep asking for value to input
    cout<<n<<"\n"; // This loop will never terminate for any Supplied val
//Above loop will terminate only when no more valued is supplied to code
// Hence once, we stopped entering the value, code will execute next line
// And end without asking for anymore value.
 cout<<"Break From Loop \n";

David G · Answer 2 · 2014-02-17T14:34:43.783

Assuming your question is "How do I resume input after the stream state has been set?" then there is a simple explanation:

The while loop in which you performed the extraction terminated only until the extraction failed; this also includes when the stream reaches the end of the input stream (EOF). When that happens the eofbit will be set in the steam state (as well as the failbit). A stream can't be used for I/O when its stream state is set. In order to use it again, the stream state must be cleared. This is done using the member function clear(std::ios_base::iostate err = std::ios_base::goodbit).

std::cin.clear();

That call will clear the bits in the stream state and assign them to 0 (std::ios_base::goodbit). After this call the stream can be used for I/O again.

This is assuming the stream read all the characters until it reached EOF. It's not sufficient for a pervious read that terminated upon the acquisition of invalid data. One would also have to ignore() the remaining characters.

std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

This doesn't work for me without an additional step to clear the bad characters. Are you sure it's sufficient? — Beta, Feb 17 '14 at 00:12
@Beta This is assuming the stream read all the characters until it reached EOF. It's not sufficient for a pervious read that terminated upon the acquisition of invalid data. One would have to `ignore()` the residual data. — David G, Feb 17 '14 at 00:14
yes that's my question, sorry for not clarifying it. however Im still a noob so I dont understand the technicalities of c++. — user3317046, Feb 17 '14 at 09:24

score 0 · Accepted Answer · answered Feb 16 '14 at 23:44

If you are not terminating the program by returning end of file (i.e. Ctrl-D) or terminating the program altogether (i.e. Ctrl-C).

That is, if you exit the loop via incorrect data type, such as typing in the letter d instead of an integer, you can follow the while loop with cin.clear() and getline(cin, str), where str is some string you declare ahead of time.

You should be able to accept input for the second cin at after this.

So,

string str;
int n;
while(cin>>n)
    cout << n << endl;
cin.clear();
getline(cin, str);
cout << "Break from loop" << endl;;
cin >> n;
cout << n;

Wow! this just works fine. Thanks! – user3317046 Feb 17 '14 at 09:21 — user3317046, Feb 17 '14 at 09:21

Cant cin after terminating the while loop

3 Answers3