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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.
What order are operations performed in, in a Perl expression?

Mathemetical operators in Perl aren't simply performed left to right - very early on your Learning to Program in Perl course you'll learn that multiplications and divisions happen before additions and subtractions, and you'll learn that brackets (also know as terms or lists) happen even earlier. Commonly this scheme - which is shared with all the other languages we teach - is referred to as BODMAS:

  Brackets
  Order (sometimes BIDMAS - "Indeces")
  Multiplication
  Division
  Addition
  Subtraction

Thus:

  $demo = 2 + 3 * 4 + 5; # see 1. below
  print "Results is $demo\n";
   
  $demo = (2 + 3) * 4 + 5; # see 2. below
  print "Results is $demo\n";
   
  $demo = (2 + 3) * (4 + 5); # see 3. below
  print "Results is $demo\n";


Will results in 19, 25, and 45, because ...

1. 3 * 4 is 12. 2 + 12 is 14. 14 + 5 is 19.
2. 2 + 3 is 5. 5 * 4 is 20. 20 + 5 is 25.
3. 2 + 3 is 5. 4 + 5 is 9. 5 * 9 is 45.

Full source of this example [here].

Remember that addition and subtraction are actually done at the same time, as are multiplication and division, so "BODMAS" is a bit of a cheat. And also remember that multiplication and division are done from left to right, thus

  $bx = 24 / 2 * 3;
gives a result of 36

but
  $bx = 24 / (2 * 3);
gives a result of 4, as does
  $bx = 24 / 2 / 3;

The majority of operations are performed left to right, but some are run right to left instead, for example =. That's how
  $g = $h = 16;
can work - 16 is assigned to $h and the result (which is a copy of the value assigned) is then assigned to $g.

Finally, for some operations the left -> right or right -> left thing doesn't make any difference, as they can't be chained - the result is of a different type. These are "nonassociative" operations.

Here's a full table of the Perl operators, listed from highest precedence (performed first) to lowest precendence, with a note of which direction they're performed in where applicable.

Operator Direction
terms and list operators (leftward) left
-> left
++ -- n/a
** right
! ~ \ and unary + and - right
=~ !~ left
* / % x left
+ - . left
<< >> left
named unary operators n/a
< > <= >= lt gt le ge n/a
== != <=> eq ne cmp ~~ n/a
& left
| ^ left
&& left
|| // left
.. ... n/a
?: right
= += -= *= etc. right
, => left
list operators (rightward) n/a
not right
and left
or xor left


If in doubt ... add some brackets!

If it gets too complicated in a single statement, consider splitting it for maintainability
(written 2011-12-07, updated 2011-12-12)

 
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)
  [2022] Pre and post increment - the ++ operator - (2009-02-03)
  [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)
  [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)

P202 - Perl Fundamentals
  [184] MTBF of coffee machines - (2005-01-20)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [1312] Some one line Perl tips and techniques - (2007-08-21)
  [1448] Question on division (Java) - Also Perl, PHP, Python ... - (2007-11-28)
  [1726] Hot Courses - Perl - (2008-07-28)
  [1826] Perl - Subs, Chop v Chomp, => v , - (2008-10-08)
  [1946] Variable Types in Perl - (2008-12-15)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [2832] Are you learning Perl? Some more examples for you! - (2010-06-27)
  [2876] Different perl examples - some corners I rarely explore - (2010-07-18)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [3102] AND and OR operators - what is the difference between logical and bitwise varieties? - (2010-12-24)
  [3278] Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. - (2011-05-05)
  [3329] Perl from basics - (2011-06-20)
  [3398] Perl - making best use of the flexibility, but also using good coding standards - (2011-08-19)
  [3574] Perl functions such as chop change their input parameters - (2012-01-10)
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [4324] Learning to program - variables and constants - (2014-11-22)


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The difference between dot (a.k.a. full stop, period) and comma in Perl
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What order are operations performed in, in a Perl expression?
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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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