Increment Letters: Weird Problem

Question

I have just asked a question on SO and found out I can make use of ++ to increment letters. I have now tried this:

$last_id = get_last_id(); echo gettype($last_id); //string echo 'L_ID ->'.$last_id.'<br />'; //AAF $next_id = $last_id++; echo 'N_ID ->'.$next_id.'<br />';//AAF

The following example which I was given works fine:

$x = 'AAZ'; $x++; echo $x;//ABA

What is going on? Must be the end of the work day...

Thanks all for any help

Paul Dixon · Accepted Answer · 2010-08-25 15:46:10Z

9

++ is a post increment operator, thus

$next_id = $last_id++;

assigns the current value of $last_id to $next_id, and then increments it. What you want is a pre-increment

$next_id = ++$last_id;

answered Aug 25, 2010 at 15:46

Paul Dixon

302k54 gold badges315 silver badges349 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

FrustratedWithFormsDesigner Over a year ago

Or he could break it into two statements: $last_id++; $next_id = $last_id;

Abs Over a year ago

Ah I did not know, that. Every time I ask a question on SO, it highlights how little I know about PHP! Thank you Paul.

FrustratedWithFormsDesigner Over a year ago

@Abs: Also, these operators exist in a number of other languages, and their behaviour there is similar.

score 3 · Accepted Answer · 2010-08-25 15:52:17Z

3

Putting ++ after a variable will increment it when the statement it's part of completes. You're assigning to $next_id the value of $last_id before it's incremented. Instead, use ++$last_id, which increments before the value of the variable is used.

edited Aug 25, 2010 at 15:52

answered Aug 25, 2010 at 15:46

Jeff Mattfield

2 Comments

Paul Dixon Over a year ago

That's not correct - the increment happens after evaluation, not when the whole statement completes. Thus $x=1; echo ($x++)*($x++); yields '2'

Paul Dixon Over a year ago

Also, operator precedence shows the order of evaluation: php.net/manual/en/language.operators.precedence.php

Collectives™ on Stack Overflow

Increment Letters: Weird Problem

2 Answers 2

3 Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Linked

Related