What is a null statement ? Explain a typical use of it
How can we use for loops when the number of iterations are not known?
You may not get useful answers to this question. This is because your
post looks like "homework", that is question that is asked in order
to
test someones knowledge of a subject they are being educated in. This
need not be (but usually is) a formal educational course. You benefit
from answering the question yourself, not by stealing the answer from
elsewhere.
For the null statement look in you text book (I suspect most
practicing
programmers couldn't give a good answer to this question; the issue
is more theoretical than practical).
Loops when the number of iterations is unknown? There must be some
sort of termination criterion. Continue looping until the criterion
is met.