If it rains we shall postpone the picnic.

Question

If it rains is a dependent clause
we shall postpone the picnic is independent. I say to put comma between rains and we, Correct?

Answer 1

I wouldn't put a comma there. It's so short, a comma isn't needed,

Answer 2

I know to use a comma when a sentence is introduced by a dependent (subordinate) clause.
Is a comma needed with two independent (subordinate) clause
Example--The classes will be held unless the schedule has been changed.

Or is, unless the schedule has been changed-----is a dependent clause.

Answer 3

No. A comma is not needed there.