How I must do the <Enter> in my program?

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Wnen I have got a new string(at time of input) my program think that it is the end of input and begin to work!

Yes your program thinks it is ed of input and begins to work, but still what do You mean with <Enter>?
Please explain it clearly.

About your <Enter> - if you talk about console, this sounds buggy. How do you read data?
Always test your program, reading files. Just comment it, when submit.

Probably you want to read the input and to understand that a line of input finished, right?

Here's a pascal program to sum up numbers till end of line:

var sum, v: longint;
begin
  sum := 0;
  while not SeekEoln do begin
    read(v);
    sum := sum + v;
  end;
  writeln(sum);
end.

P.S. As for C++, guys, please give an example with cin.