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# Comma operator and order or precedence

Posted on 2013-12-11

Ah hello.

I am sure I am having a silly moment here, but I am trying to understand the comma operator in C++ and "operator precedence" rules (which I believe are a general maths thing, hence me posting this in the Maths TA too:)).

From what I have read about the comma operator, we have two facts

1) The result of it is the right hand value, so for example a,b would yield b.

2) It has the lowest operator precedence. I read this means "it's always the last one to bind to an expression", but I don't quite get that bit.

So, if we have

a = (b , c)

the evaulation sequence would first be (b,c) which would yield c, hence a would be assigned c. But I am struggling with

a = b , c

This is apparently equivalent to

(a = b) , c

The result of this expression is b.

Now, I know we have to evaluate the brackets first, which results in b, so we then have

b, c

Q1) From rule 1 above, why is the result hence not c? Clearly something is incorrect in what I deduced above, but I cannot see it...

Q2) Can someone clarify fact 2) above and what "it's always the last one to bind to an expression" means?

TIA