Question: Hide several exp statements after if then

How can several expression statements be not displayed during and after an execution process of "then"conditional statement (I mean "If.....then...")?
For example:

if .... then
exp1:
exp2:
exp2:
....... 

end if;

each expression above can consist of various commands in its body.All my exp statements were finished by ":"
but, they were still displayed after execution, some even showing the calculation process and all the varables attained.
I only want that some exp's are to be shown and others not. How to make that?

Thanks 

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