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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.
Increment operators for counting - Perl, PHP, C and others

Look at this Perl statement:
  $counter = $counter + 1;
"Take the value in $counter, add 1 to it, and put it back in $counter". It's a common programing requirement - indeed, so common that you can write it in a shorter form in many languages:
  $counter += 1;
"Add one to the value led in $counter and store the result there". And when you think about it, there's even a word in English for adding 1 - "increment"; many languages (Perl, PHP, C, C++, Ruby, Java ...) have adopted a special syntax for it too:
  $counter++

There's an example of this shortening - and other shortenings - on our Perl Programming Course which I've been running in a tailored, single company form today. The original example is [here] and the example showing the shortenings is [here].

Some people (class discussion point - "is this good programming practice?") go a stage further and write statements such as:
  $oc = $counter++;
or
  $nc = ++$counter;
Which is going to save the value of counter into a new variable, and also to increment (step it up by one). But beware - there is a difference in what happens here.

• If you write
  $nc = ++$counter;
then $counter is pre-incremented - in other words, it's increased before a copy is saved into $nc. So - for example - incoming value of $counter is 15, then the outgoing value is also 15 and $nc also gets the value 15

• But if you write
  $oc = $counter++;
then $counter is post-incremented - in other words, it's only increased after a copy hash been saved into $oc. So - for example - incoming value of $counter is 15, then the outgoing value is also 15 and $oc gets the old value of 14

Personal advise - if in doubt, write it as 2 lines:
  $cv = $counter;
  $counter++;
or
  $counter++;
  $cv = $counter;
then you'll be sure whether the copy was taken before or after the increment.

Notes:

1. There's also a -- operator (decrement) which uses the same principles in each of the languages I have mentioned

2. One of the most powerful uses of ++ is to increment an array of counters - as you can see [here] in a PHP course example which counts the number of times each picture has been viewed on our web site

3. In C, the ++ operator increments variables that contain integers by 1 as you would expect (example [here]), but if you use it to increment a pointer then the pointer will be stepped up by the size of the variable that's pointed to. So on must C compilers,
  float *quack;
  quack++;

will add 4 to the value held in quack (32 bit float = 4 bytes).

If you're new to C, but have programmed before in another language we offer a C programming course [here]. We also offer a course in C programming for newcomers to programming ([here]) and C++ courses ([here])
(written 2010-10-18, updated 2010-10-20)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P204 - Perl - Conditionals and Loops
  [353] Wimbledon Neck - (2005-06-20)
  [930] -> , >= and => in Perl - (2006-11-18)
  [1191] Smart English Output - via PHP and Perl ? : operator - (2007-05-18)
  [1468] Lexical v Arithemetic testing, Bash and Perl - (2007-12-11)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1607] Learning to program in Perl - (2008-04-11)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1727] Equality and looks like tests - Perl - (2008-07-29)
  [2351] Ternary operators alternatives - Perl and Lua lazy operators - (2009-08-12)
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2832] Are you learning Perl? Some more examples for you! - (2010-06-27)
  [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)
  [4031] Showing what programming errors look like - web site pitfall - (2013-03-06)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)

H106 - PHP - Arrays
  [409] Functions and commands with dangerous names - (2005-08-11)
  [603] PHP - setting sort order with an associative array - (2006-02-13)
  [773] Breaking bread - (2006-06-22)
  [832] Displaying data at 5 items per line on a web page - (2006-08-14)
  [1116] PHP adding arrays / summing arrays - (2007-03-23)
  [1199] Testing for one of a list of values. - (2007-05-22)
  [1451] More PHP sample and demonstration programs - (2007-12-01)
  [1614] When an array is not an array - (2008-04-17)
  [2215] If nothing, make it nothing. - (2009-06-02)
  [2274] PHP preg functions - examples and comparision - (2009-07-08)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2920] Sorting - naturally, or into a different order - (2010-08-14)
  [3379] Sorting data the way YOU want it sorted - (2011-08-05)
  [3534] Learning to program in PHP - Regular Expression and Associative Array examples - (2011-12-01)
  [4068] Arrays in PHP - contain different and even mixed data types - (2013-04-24)
  [4072] Splitting the difference with PHP - (2013-04-27)
  [4244] Disambiguation - PHP List - (2014-03-07)

C207 - C and C based languages - Pointers and references
  [1155] Pointers in C - (2007-04-19)
  [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19)
  [1497] Training Season Starts again! - (2008-01-07)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2572] The what and why of C pointers - (2010-01-13)
  [2670] Pointers to Pointers to Pointers - what is the point? - (2010-03-10)
  [3121] New year, new C Course - (2011-01-05)
  [3238] Bradshaw, Ben and Bill. And some C and C++ pointers and references too. - (2011-04-09)
  [3242] How to return 2 values from a function (C++ and C) - more uses of pointers - (2011-04-10)
  [3386] Adding the pieces together to make a complete language - C - (2011-08-11)
  [3399] From fish, loaves and apples to money, plastic cards and BACS (Perl references explained) - (2011-08-20)
  [4128] Allocating memory dynamically in a static language like C - (2013-06-30)
  [4560] Variables, Pointers and References - C and C++ - (2015-10-29)

C203 - C and C based languages - Conditionals and Loops
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [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)
  [2002] New C Examples - pointers, realloc, structs and more - (2009-01-20)
  [2570] Function Prototypes in C - (2010-01-11)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [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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Lots of ways of doing it in Perl - printing out answers
Some other Articles
Dulwich College Preparatory, and Sevenoaks, Schools
Setting up a matrix of data (2D array) for processing in your program
Santa announcement, 5th December 2010, Melksham
Lots of ways of doing it in Perl - printing out answers
Increment operators for counting - Perl, PHP, C and others
What will we be teaching in six years?
A list of special method and attribute names in Python
How will we present courses over the coming years?
Looking forward - the next 3000
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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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