Hi hoa20101988,
I accept with the previous answer but I want to explain the reason :
There is some symbols which can not be written as it is between the quotes like
", /, \, ', enter key, tab key
and others where you have to put before them: \
enter key
would be \n ,
tab key
\t
when you you are writting it as string between 2 quotes.
this
link[
^] can give you more information.
I hope this help,
:)