Question

help in increment and decrement operators in c language?
example --a means?

Answer 1

--a
is the same as
a--
except that in the prior the subtraction operation is carried out before other operators (logical comparisons, etc)
a--
is the same as
a-=1
is the same as
a=a-1

Answer 2

--a is a pre-decrement . a is decremented and then evaluated. a-- is post-decrement. a is evaluated and then decremented. I'll leave the increments (++) to you.