The only difference between n++ and ++n is that n++ yields the original value of n, and ++n yields the value of n after it’s been incremented. Both have the side effect of modifying the value of n by incrementing it.
If the result is discarded, as it is in your code, there is no effective difference.
If your program is behaving differently depending on whether you write
n++;
or
++n;
it must be for some other reason.
In fact, when I compile and execute your program on my system, I get exactly the same output in both cases. Adding newlines to the output format, I get:
At n = 25, Algorithm A performs in 114661785600 seconds & Algorithm B performs in 282429536481 seconds.
You haven’t told us what output you’re getting. Please update your question to show the output in both cases.