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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.
Question Mark - Colon operator (Perl and PHP)

The ? and : operator in Perl and PHP allows you to write a single statement that's both an if and an else without the need for all the clutter of keywords, extra variables, and so on if all you want to do is come up with two alternative words.

Here's an example in PHP - throwing a number on a die, and telling the user to proceed if the value thrown is a five or six, but to try again is it's a 1, 2, 3 or 4:

<?php
 
# Throw a die
 
$throw = rand(1,6);
 
print ("You threw a $throw which means you should ".
  (($throw > 4) ? "proceed" : "try again").
  " at the next turn\n");
 
?>


Here's how it works ("all our code is tested" as I wrote in an email to someone yesterday!)

Dorothy:p1 grahamellis$ php pz
You threw a 3 which means you should try again at the next turn
Dorothy:p1 grahamellis$ php pz
You threw a 6 which means you should proceed at the next turn
Dorothy:p1 grahamellis$


Here is the same functionallity using if and else:

<?php
 
# Throw a die
 
$throw = rand(1,6);
 
if ($throw > 4) {
  $action = "proceed";
} else {
  $action = "try again";
}
 
print ("You threw a $throw which means you should ".
  "$action at the next turn\n");
 
?>


In Perl (I'm running a Learning to Program in Perl course this week, which is where this article originated!), you have the same thing - and a wide variety of other convenient alternatives to if for conditionals and while for loops. I've posted up an example that uses until and also the ? : pairing at http://www.wellho.net/resources/ex.php4?item=p206/golf ... in this demonstration, you enter the number of individuals or teams you have signed up for a knock out competition, and the program tells you what your target should be if you want a perfect knockout with no need for any "byes" in the first round. Here it is running:

Dorothy:p1 grahamellis$ perl golf
How many people? 6
You really need 8
Dorothy:p1 grahamellis$ perl golf
How many people? 8
You're fine as you are with 8
Dorothy:p1 grahamellis$ perl golf
How many people? 11
You really need 16
Dorothy:p1 grahamellis$


You'll note - once again - the subtle use of ? : in the code to change the text "you'll really need ..." into "you're fine as you are with ..." - oh the power of Perl and its plethora of operators.
(written 2008-10-08)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P206 - Perl - More Loops and Conditionals
  [138] Perl - redo and last without a loop - (2004-12-02)
  [299] What - no switch or case statement? - (2005-05-03)
  [657] The ternary operator in Python - (2006-03-25)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [1191] Smart English Output - via PHP and Perl ? : operator - (2007-05-18)
  [1220] for loop - how it works (Perl, PHP, Java, C, etc) - (2007-06-06)
  [1582] Ruby, C, Java and more - getting out of loops - (2008-03-19)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2815] switch and case, or given and when in Perl - (2010-06-17)
  [2817] Setting a safety net or fallback value in Perl - (2010-06-19)
  [2824] A pint of Black Rat, and a lazy barman - (2010-06-25)
  [2832] Are you learning Perl? Some more examples for you! - (2010-06-27)
  [2892] Alternative loops and conditionals in Ruby and Perl - (2010-07-28)
  [2967] Multiway branches in Perl - the given and when syntax - (2010-09-22)
  [2972] Some more advanced Perl examples from a recent course - (2010-09-27)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3398] Perl - making best use of the flexibility, but also using good coding standards - (2011-08-19)
  [3619] Ruby v Perl - a comparison example - (2012-02-21)
  [3914] While, for, foreach or something else to loop. - (2012-11-06)

H104 - PHP - Control Statements
  [340] Code and code maintainance efficiency - (2005-06-08)
  [353] Wimbledon Neck - (2005-06-20)
  [406] Assignment, equality and identity in PHP - (2005-08-08)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [863] Double and Triple equals operator in PHP - (2006-09-12)
  [1199] Testing for one of a list of values. - (2007-05-22)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [2304] Extracting real data from an exported file in PHP or Perl - (2009-07-25)
  [2912] Predictions for the seagull population - (2010-08-09)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3895] Flowchart to program - learning to program with Well House - (2012-10-14)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)


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Perl - Subs, Chop v Chomp, => v ,
Some other Articles
Dont bother to write a Perl program
Perl - map to process every member of a list (array)
What a shock
Perl - Subs, Chop v Chomp, => v ,
Question Mark - Colon operator (Perl and PHP)
Which is your best hotel room?
FSB - an update.
Claverton Pump
Autumn
Sorting objects in PHP
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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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