I want to know if there is any generic statement that can clear all the variables' values within a for loop once the loop ends.
NO, there is not.
I am using a lot of variables inside sim_cnt which are vectors and whose shapre change as 'n' changes.
You should be pre-initializing all of the variables anyhow. Any variable that you already assign zeros or nan or whatever to, of proper length according to the current n, is already properly set up to not need to be cleared. Any variable whose previous value would interfer with use in the new iteration (such as because it is potentially the wrong size) should be initialized because it is inefficient to grow variables dynamically.
.. But if you really need to do this for some reason, adopt a naming convention for the variables inside the loop, and use clearvars with either the * wildcard or the -regexp option.
