alireza,
you really should work through the
Serial Input Basics Tutorial
Additionally to receive a better and more detailed help you should post an example of what you want to enter
I will use the #-symbol to mark beginning and end of the characters to enter. This means only the characters between the leading and trailing "#" are the real input
Examples:
Do you want to enter #200# ?
Do you want to enter #200++# ?
Do you want to enter #30+40# ?
No idea. Because you haven't posted examples yet
best regards Stefan