ah,how can I get the “spare parameter” in H12 ?
This picture is a screenshot from a data , and it was worked in H8 ;
Or how to get it's effect in H12 ?
The box's expression is icmax(0,$C),what should I do in H12 to have the same effect ?

this spare parameter just contains the maximum value per each channel from first input (icmax(0,$C))
but on its own it does nothing, just stores that value, it is probably referenced in other parameters of that node
so you have 2 options, put icmax(0,$C) directly instead of it's references and in that case you don't have to create it
or
create it and reference in that parameters to get the same effect

this may help if you are asking about the process of creating spare parm itself
http://www.sidefx.com/docs/houdini12.1/ref/windows/edit_parameter_interface#id439637 [sidefx.com]

Thank you very much , gentleman .