It is related to C programming language. Can anybody explain side effects and sequence points in easy language?

Question

And why the pre-increment operator is well defined in C language (what are the reasons behind it) why not the post?
Example :
int main() {
int a=10;
printf("%d %d %d\n", a++, a++, a++) ;
int b = 10;
printf("%d %d %d", ++b, ++b, ++b) ;
return 0;}

Output:
12 11 10
13 13 13

Acc. To C standards, the order of evaluation of the arguments in a function call is unspecified. So the order in which the three a++ evaluated is not guaranteed.
But how the value for ++b is evaluating ? //The behavior is well defined for the pre-increment operator// okay.

When the same program runs using volatile keyword then the value of ++b gets evaluated as
13 12 11..

I am so much confused here between volatile and without volatile.

Answer 1

You don't even need to drag volatile into this to get more confusion. Just try to run the same snippet on various C compiler, then you'll see that your statement "behaviour of pre-increment operator is well defined" might need a revision cause the output may vary.

The subjects you asked for (side effect and sequence point) is rather a difficult subject to explain, I wouldn't dare myself to even try.

Wiki has some info on those subjects ...

https://en.m.wikipedia.org/wiki/Side_effect_(computer_science)

https://en.m.wikipedia.org/wiki/Sequence_point

https://en.m.wikibooks.org/wiki/C_Programming/Side_effects_and_sequence_points

I don't know whether they wrote it in easy language for the readers, but it might make a good intro.