Can you tell me what'll happen if I write to the output
without reading all of the input and then continue reading
the input?
There're problems which have inputs that may consist of
more than one test.In such cases the answers of the
different tests take up too much memory.

Thank you for the help in advance

We run your program in the way
program.exe  < test.in  > answer.out
so i don't think you should first reqad, then write -
you can do it when you like .