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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.
Assigning values to variables within other statements - Ruby

In Ruby, and in Perl too, you can use assignments within other statements and in so doing perform two distinct actions in one line of code. Here's what I mean (using irb - interactive Ruby):

  >> j = 16
  => 16
  >> print "The value is #{k=j} at the moment"
  The value is 16 at the moment=> nil
  >> print k
  16=> nil
  >>


... you'll notice that I've both printed out a line of text including the value of the variable j, and copied it to the variable k, in a single statement.

Operations such as this can also effect the incoming variables, and where they do you need to take care to ensure that you know whether the second use of the variable's value wil be made before or after it is changed. Look at this statement:

  print "#{now+=1}"

... and ask yourself whether it will be the old value of now, or the new one, that's printed out, And again - in

  bob = now += 4

will bob be assigned to a copy of the incoming value of now, or the outgoing value once 4 has been added?

In general, the answer to the question "what happens first" comes down tho the languages's precedence tree and any bracketting you have in there (there are some catches with how opertors like += and Perl's ++ interact with brackets). And in general, I'm going to advise that you should usually write the code as two lines if you want to perform two actions.. By separating the operations, you may be making the code a little longer, but you're also making it unambiguous to the inexperienced reader who may come along to maintain the code later. And you're also going to save yourself any problems if you're required to remove one but not both of the operations performed at a later date.

Scenario ... the boss comes along. "Great program, Graham, but a bit verbose on its output. Can you remove the step logging as it run?" So I delete the print statment that I've shown above .. and then the whole program fails as I've also removed the secondary effect of increasing now. Oops!

Full source code example including the statements above - [here]. There's also sample output so you can see how it ran, and what the order was.
(written 2011-09-07)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
R104 - Ruby - Control Structures
  [960] 1st, 2nd, 3rd revisited in Ruby - (2006-12-02)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [985] Equality in Ruby - == eql? and equal? - (2006-12-14)
  [995] Ruby's case - no break - (2006-12-17)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [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)
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1738] Clean code, jump free (Example in Lua) - (2008-08-06)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1887] Ruby Programming Course - Saturday and Sunday - (2008-11-16)
  [1891] Ruby to access web services - (2008-11-16)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [2287] Learning to program in Ruby - examples of the programming basics - (2009-07-15)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2619] Passing code to procedures and yield in Ruby - (2010-02-02)
  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2892] Alternative loops and conditionals in Ruby and Perl - (2010-07-28)
  [2975] Why do I need brackets in Ruby ... or Perl, Python, C or Java - (2010-09-29)
  [3156] Splitting data reading code from data processing code - Ruby - (2011-02-04)
  [3158] Ruby training - some fresh examples for string handling applications - (2011-02-05)
  [3159] Returning multiple values from a function call in various languages - a comparison - (2011-02-06)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3253] Is this number between? Does this list include? - Ruby - (2011-04-18)
  [3254] Multiple inputs, multiple out, ruby functions - (2011-04-19)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3619] Ruby v Perl - a comparison example - (2012-02-21)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3769] Muttable v immutable and implications - Ruby - (2012-06-20)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4370] Conditionals, loops and methods in Ruby - a primer with simple examples - (2014-12-29)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4503] Separating your code for easier testing, understanding and re-use; example in Ruby - (2015-06-02)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)
  [4674] Alternating valuses / flip-flop / toggle - example in Ruby - (2016-05-17)


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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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