Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!ll-xn!husc6!ut-sally!im4u!halley!bc
From: bc@halley.UUCP (Bill Crews)
Newsgroups: comp.lang.c
Subject: Re: Associativity -- what is it?
Message-ID: <329@halley.UUCP>
Date: 24 Feb 88 02:40:28 GMT
References: <226@mccc.UUCP> <224@sdrc.UUCP> <234@mccc.UUCP>
Reply-To: bc@halley.UUCP (Bill Crews)
Organization: Tandem Computers, Austin, TX
Lines: 42

In article <234@mccc.UUCP> pjh@mccc.UUCP (Peter J. Holsberg) writes:
>In article <224@sdrc.UUCP> scjones@sdrc.UUCP (Larry Jones) writes:
>|In article <226@mccc.UUCP>, pjh@mccc.UUCP (Peter J. Holsberg) writes:
>|> 
>|> 	x = 3 * i ++;
>|> 
>|> Book says that ++ has a higher precedence than *, and that ++
>|> associates from R->L.  That makes me think that ++ should be applied
>|> first, but I know it isn't.  But ????
>|
>|But ++ IS applied first!  The key point here is that the RESULT of postfix
>                                                          ^^^^^^^^^^^^^^^^^
>|++ is the value BEFORE incrementation, not that postfix ++ is somehow deferred
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>|until later.
>
>Well, that still leaves me confused.  If i has the value 7, it is 7 that
>is added to 3, so it seems to be that the ++ *is* deferred until later. 
>Also, ++ has higher precedence than +, so why is the incrementation
>delayed until after the current value of i is used?

Here is how to think of it.  ++ performs two functions.  It returns a value,
and it has an effect on the variable to which it is applied.

If the ++ precedes its operand:

	it increments the operand
	it returns the resulting value

If the ++ succeeds its operand:

	it increments the operand
	it returns the value of the operand prior to the increment

The other operators with which you are comparing it have only the functions of
returning a value.  This makes it confusing.  But the act of returning the
previous value is quite different from deferring the operator's effect.

-bc
-- 
Bill Crews                                   Tandem Computers
bc@halley.UUCP                               Austin, Texas
..!rutgers!im4u!halley!bc                    (512) 244-8350