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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.
How a for loop works Java, Perl and other languages

Java, Perl, PHP, Ruby, C, C++, Tcl and many other languages support a "for" loop construct.

When your program enters the top of the loop, it performs the first statement in the brackets ... in this Perl example, that's to initialise the $now variable to 1. It then evaluates the expression given as the second element in the brackets - in the example checking if $now is less that or equal to 12. If that's true, the block is performed; if it's false, the program carries on running after the block.

If the block is performed (it doesn't have to be - a for loop's block may run zero times!), the third and final statement in the initial brackets is performed after the block - that adds one to $now in the example - and then the test in the second item (the expression) is performed again. And again, if that's true, the block is performed; if it's false, the program carries on running after the block.

You COULD do without a for loop ... move the first statement in the brackets above the loop code, change for to while and move the last statement inside the block as its very last statement. But that makes for three statements rather than one ... and code that's going to much harder to follow if you have to come back and update it later.

They say "imitation is the sincerest form of flattery" ... so I'm flattered by Martin Naughon's web site ([here]) which uses my diagram to illustrate the for loop. Actually, my feeling flattered also left me feeling slightly peeved initially because I've not been asked for permission, but that has now been sorted out between us. And - talk about mixed emotion - I'm open-mouthed at Martin's text which - reads "A lot of people do not know exactly how the for loop works in Java or Perl but they know how to make it work for them. Developers usually make it work through trial and error. The picture below illustrates exactly how a for loop works with arrows. If you know this picture, it will help you with some questions in the Sun Certified Java Programmer exam.". Martin - I hadn't realised how poorly informed most programmers were, nor how trivial the questions are in the Java Certification exams; actually, I think you're wrong in your view of the knowledge of most of our fellow programmers.

We cover the for loop on all of our programming courses - see [here].


Note - the for loop in Python does NOT work in the way described above - there's a commented example [here] stepping up through a range, and another Python example [here] that iterates through a list.
(written 2011-03-12, updated 2014-02-02)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y103 - Python - Conditionals and Loops
  [299] What - no switch or case statement? - (2005-05-03)
  [353] Wimbledon Neck - (2005-06-20)
  [657] The ternary operator in Python - (2006-03-25)
  [668] Python - block insets help with documentation - (2006-04-04)
  [788] New - Conditional expressions in Python 2.5 - (2006-07-01)
  [835] Python - when to use the in operator - (2006-08-16)
  [909] Python is like a narrowboat - (2006-10-30)
  [1201] No switch in Python - (2007-05-23)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1661] Equality, sameness and identity - Python - (2008-05-31)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [2899] Groupsave tickets - 3 or 4 train tickets for the price of 2 - (2010-08-02)
  [3083] Python - fresh examples from recent courses - (2010-12-11)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3439] Python for loops - applying a temporary second name to the same object - (2011-09-14)
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3762] Learning to program - the if statement. Python. - (2012-06-12)
  [3895] Flowchart to program - learning to program with Well House - (2012-10-14)
  [4092] Identity in Python - (2013-05-17)
  [4210] If elif elif elif - multiway selection in Python - (2013-11-16)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4541] Setting up and tearing down with the Python with keyword - (2015-10-16)
  [4545] Method, Class, Module, Package - how to they relate in Python? - (2015-10-17)
  [4713] Equality (in Python) - (2016-10-30)
  [4723] Conditional operators in Python - (2016-11-05)

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)
  [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)
  [3253] Is this number between? Does this list include? - Ruby - (2011-04-18)
  [3254] Multiple inputs, multiple out, ruby functions - (2011-04-19)
  [3422] Assigning values to variables within other statements - Ruby - (2011-09-07)
  [3619] Ruby v Perl - a comparison example - (2012-02-21)
  [3769] Muttable v immutable and implications - Ruby - (2012-06-20)
  [4370] Conditionals, loops and methods in Ruby - a primer with simple examples - (2014-12-29)
  [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)

P206 - Perl - More Loops and Conditionals
  [138] Perl - redo and last without a loop - (2004-12-02)
  [1191] Smart English Output - via PHP and Perl ? : operator - (2007-05-18)
  [1825] Question Mark - Colon operator (Perl and PHP) - (2008-10-08)
  [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)
  [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)
  [3398] Perl - making best use of the flexibility, but also using good coding standards - (2011-08-19)
  [3914] While, for, foreach or something else to loop. - (2012-11-06)

J704 - Java - Loops and Conditional Statements
  [2734] for and foreach in Java - (2010-04-22)
  [3038] Setting up individual variables, and arrays, in Java - some commented examples - (2010-11-09)
  [4346] A behaviour driven example of writing a Java program - (2014-12-09)
  [4427] Java example - for loop and conditionals from course exercise - (2015-02-16)

H104 - PHP - Control Statements
  [340] Code and code maintainance efficiency - (2005-06-08)
  [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)
  [2304] Extracting real data from an exported file in PHP or Perl - (2009-07-25)
  [2912] Predictions for the seagull population - (2010-08-09)

C203 - C and C based languages - Conditionals and Loops
  [2002] New C Examples - pointers, realloc, structs and more - (2009-01-20)
  [2570] Function Prototypes in C - (2010-01-11)
  [3004] Increment operators for counting - Perl, PHP, C and others - (2010-10-18)
  [3121] New year, new C Course - (2011-01-05)
  [3243] Breaking the running sequence - an introduction to conditional statements and loops - (2011-04-11)
  [3384] Loops - a comparison of goto, while and for - (2011-08-10)
  [4337] Learning to program sample program - past its prime, but still useful - (2014-12-02)


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A change to the Well House team - thank you and good luck, Chris
Some other Articles
Two views of a war memorial
Melksham Town Council announces ...
Telling you something about us in just one line
A change to the Well House team - thank you and good luck, Chris
How a for loop works Java, Perl and other languages
Lunch for Melksham Businesses
TransWilts rail - coming together, wanted and needed
Finding and diverting image requests from rogue domains
No news is good news.
Sunny day - Clanger and Picket Woods, Shearwater, and Westbury
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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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