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Conditionals, loops and methods in Ruby - a primer with simple examples

Continuing with my basic Ruby update - a lot of examples on control structures at [this link].

Conditionals in Ruby include if, unless and case (the equivalent of a switch statement. It's been argued that for a strongly object oriented language a "switch" type structure is not needed, and indeed encourages coding away from the language paradigm. However, in the case of ruby one has been provided (compare and contrast to Python!). See example of each syntax [here]. Ruby also supports "lazy operators" which are in effect conditionals - see an example [here].

In any condition, the question "what does equality mean" may arise, and in ruby there are four ways of asking the question:
== - equal in value
=== - Used to test equality within a when clause of a case statement
.eql? - same type AND equal in value
.equal? - the same object
See example [here]

loops come in number of varients too - see examples of for and each loops [here], and note the double and triple dot operators:
1..20 - 1 to 20, including 20
1...20 - 1 to 20, excluding (stopping short of) 20
There's a while loop - write it forward (the conventional way [here]) or backward as shown [here] and even a loop statement without a condition that you must break out of - [here] ... see a real use of it [here] when I keep re-prompting the user for input until he enters a valid reply. If you want the negative condition, replace "while" with "until".

named blocks of code are know as "methods" and are defined using a def keyword. There's a first simple example [here] and one showing an optional (defaulted) parameter [here]. Methods can even be redefined "on the fly" - not always a good thing, but useful in some circumstances - see [here].

As well as methods with conventional return statements, Ruby supports generators which will yield a series of results in succession - see [here] for an example of the definition and use of such a function.

I'm starting the new year with a private Ruby course ... and open for further bookings right through the year. There's one week available in January, nothing in February (sorry - fully booked), and one week in May. March, April and June onwards are fairly open at the moment. Public course are provisionally set to start on 20th April, 13th July and 19th October ... the latter dates may change, but we work on the basis that once we get even just a single booking for the course they're fixed and guaranteed to run. See [here] for course details
(written 2014-12-29, updated 2014-12-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
R104 - Ruby - Control Structures
  [4674] Alternating valuses / flip-flop / toggle - example in Ruby - (2016-05-17)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)
  [4503] Separating your code for easier testing, understanding and re-use; example in Ruby - (2015-06-02)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [3769] Muttable v immutable and implications - Ruby - (2012-06-20)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3619] Ruby v Perl - a comparison example - (2012-02-21)
  [3422] Assigning values to variables within other statements - Ruby - (2011-09-07)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3254] Multiple inputs, multiple out, ruby functions - (2011-04-19)
  [3253] Is this number between? Does this list include? - Ruby - (2011-04-18)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3159] Returning multiple values from a function call in various languages - a comparison - (2011-02-06)
  [3158] Ruby training - some fresh examples for string handling applications - (2011-02-05)
  [3156] Splitting data reading code from data processing code - Ruby - (2011-02-04)
  [2975] Why do I need brackets in Ruby ... or Perl, Python, C or Java - (2010-09-29)
  [2892] Alternative loops and conditionals in Ruby and Perl - (2010-07-28)
  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2619] Passing code to procedures and yield in Ruby - (2010-02-02)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2287] Learning to program in Ruby - examples of the programming basics - (2009-07-15)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [1891] Ruby to access web services - (2008-11-16)
  [1887] Ruby Programming Course - Saturday and Sunday - (2008-11-16)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1738] Clean code, jump free (Example in Lua) - (2008-08-06)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [1582] Ruby, C, Java and more - getting out of loops - (2008-03-19)
  [1220] for loop - how it works (Perl, PHP, Java, C, etc) - (2007-06-06)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [995] Ruby's case - no break - (2006-12-17)
  [985] Equality in Ruby - == eql? and equal? - (2006-12-14)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [960] 1st, 2nd, 3rd revisited in Ruby - (2006-12-02)


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Some other Articles
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Why are people using the TransWilts?
Conditionals, loops and methods in Ruby - a primer with simple examples
Ruby - the second rung of learning the language
Shuffling a list - Ruby and Python
A year of rail memories!
Changing what operators do on objects - a comparison across different programming languages
The changing face of Christmas
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