Re: Increment and decrement operators

["R. Bruce Hoffman, Jr." <rbruceh@xxxxxxxxxxxxx>]

-----Original Message-----
From: teresa garcia <teresa_a_garcia@hotmail.com>
To: JAVA400-L@midrange.com <JAVA400-L@midrange.com>
Date: Monday, July 10, 2000 3:54 PM
Subject: Increment and decrement operators


>Please, please, someone please help me understand why this two expressions
>are not equivalent:
>
>a[i++]++
>a[i++]=a[i++] + 1;
>
>The books I have only state they are not equivalent, I am suppose to guess
>the rest, but I don't find it trivial.


And it isn't, trivial that is, but...

in the second statement, the i++ is used and incremented twice.  On the RHS,
the expression is completely evaluated prior to assignment, so i is
incremented, _prior_ to the assignment.  I on the LHS is now one greater
than it was just prior to the evaluation of the RHS.

so... the first statement uses i to index and bumps that a[i].
and... the second uses i to index and bumps i and then uses that i again
(now bumped by one) to index the a[i] on the left.

clear?  maybe...

plug this code into a class and it's main...

    int [] a = new int[3];

    a[0] = 1;
    a[1] = 1;
    a[2] = 1;

    int i = 0;

    System.out.println("a[0] =" + a[0] + " a[1] =" + a[1] + " i =" + i);
    a[i++]++;
    System.out.println("a[0] =" + a[0] + " a[1] =" + a[1] + " i =" + i);
    a[i++]=a[i++] + 1;
    System.out.println("a[0] =" + a[0] + " a[1] =" + a[1] + " i =" + i);

then run it.  That may help..

ta.
===========================================================
R. Bruce Hoffman, Jr.
 -- IBM Certified AS/400 Professional System Administrator
 -- IBM Certified AS/400 Professional Network Administrator
 -- IBM Certified Specialist - AS/400 Administrator
 -- IBM Certified Specialist - RPG IV Developer

"Those who would give up essential Liberty,
  to purchase a little temporary Safety,
  deserve neither Liberty nor Safety."

     - The Papers of Ben Franklin


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