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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Pre and post increment - the ++ operator

The ++ (increment) operator in PHP (and Perl, and C, and Ruby) adds one to the value held in a variable and saves the result back in the same variable. But you'll see both $n++; and ++$n; in code. What is the difference?

If you write the ++ in front of the variable name, the variable is incremented before it is used for anything else in the context it is written (know ad a pre-increment), but if it is written after the variable name, the existing contents of the variable are used for anything else that's done in the content and the variable is then increments - a post increment. Look at this example:

<?php
$f = 6 + 7; # 1
$k = $f++; # 2
$m = ++$f; # 3
$g = 8 + 9;
$h = $f . $g; # 4
print "$h $k $m\n";
?>


The line #1 sets the variable $f to 13.

Line #2 sets $k to the contents of $f (13) and THEN increments $f to make it 14. A postincrement.

Line #3 increments $f and THEN stores the result (now 15) into $k. A preincrement

So the code runs like this:

Dorothy:f9php grahamellis$ php silly
1517 13 15
Dorothy:f9php grahamellis$


Some Notes

1. In C, if you use ++ on a pointer variable, it will increment it by one memory address and thus provide you with a way of incrementing through an array. If you write

int * mypointer;
...
mypointer++;


You will actually add two or four to the variable, depending on whether you are compiling with 2 byte or 4 byte integers (the latter is he default in most systems these days)

2. The -- operator (decrement) behaves in the same way

3. As good programming practise in code that you're writing for maintainance by casual or inexperienced programmers, you should consider writing the assignment and increment as two separate operations - for example, code a postincrement as:

$m = $f; $f++

4. If you want to increment by a different amount, use the += operator in any of the languages that I have mentioned so far:

$days += 5;

5. Python does NOT support the ++ operator, but it does support +=

6. You will find that most languages that we teach also support -=, *=, /=, %= ... and even more similar operations. Here's a Perl example:

$agemlimit ||=18;

Which sets $agelimit to 18 unless it already has a non-zero value, Neat, huh, but pity the newcomer!

Line #4 shows how the . operator concatenates strings in PHP ... even if the incoming variables are both integers. The type conversion is automatic.
(written 2009-02-03)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Q101 - Object Orientation and General technical topics - Programming Principles
  [2001] I have not programmed before, and need to learn - (2009-01-19)
  [2228] Where do I start when writing a program? - (2009-06-11)
  [2310] Learning to write high quality code in Lua - (2009-07-30)
  [2327] Planning! - (2009-08-08)
  [2415] Variable names like i and j - why? - (2009-09-22)
  [2510] The music of the stock market - (2009-11-22)
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2586] And and Or illustrated by locks - (2010-01-17)
  [2737] Improving your function calls (APIs) - General and PHP - (2010-04-24)
  [2769] Easy - but for whom? - (2010-05-18)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2964] An introduction to file handling in programs - buffering, standard in and out, and file handles - (2010-09-21)
  [3026] Coding efficiency - do not repeat yourself! - (2010-11-02)
  [3456] Stepping stones - early coding, and writing re-usable code quickly - (2011-09-24)
  [3542] What order are operations performed in, in a Perl expression? - (2011-12-07)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3551] Some terms used in programming (Biased towards Python) - (2011-12-12)
  [3673] Object oriented or structured - a comparison in Python. Also writing clean regular expressions - (2012-03-26)
  [3878] From Structured to Object Oriented Programming. - (2012-10-02)
  [3928] Storing your intermediate data - what format should you you choose? - (2012-11-20)
  [3954] Lesson 1 in programing - write clean, reuseable and maintainable tidy code - (2012-12-16)
  [4003] Web and console - same principle, same code - Ruby example - (2013-02-14)
  [4061] Seamless, integrated IT - we have a long way to go! - (2013-04-11)
  [4090] Test Driven Development in Python - Customer Comes First - (2013-05-16)
  [4118] We not only teach PHP and Python - we teach good PHP and Python Practice! - (2013-06-18)
  [4153] Rooms available tonight - how to code an algorithm from first principles - (2013-08-19)
  [4206] Writing the perfect program in Tcl? - (2013-11-13)
  [4325] Learning to program - what are algorithms and design patterns? - (2014-11-22)
  [4611] Hungarian, Camel, Snake and Kebab - variable naming conventions - (2016-01-03)
  [4632] Remember to ask the question before you listen for the answer - (2016-01-26)
  [4645] What are callbacks? Why use them? An example in Python - (2016-02-11)

P258 - Perl - Solaris, OSX and Linux
  [1633] Changing a screen saver from a web page (PHP, Perl, OSX) - (2008-05-06)
  [1702] Running operating system commands in Perl - (2008-07-08)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)


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sw_vers - what version of OSX am I running?
Pre and post increment - the ++ operator
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Learning Python - many new example programs
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UnboundLocalError - Python Message
Python - a truly dynamic language
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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