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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.
BODMAS - the order a computer evaluates arithmetic expressions

What order does a computer program use to evaluate expressions? If I write
  2 + 3 * 4 + 5
does it start off, left to right ...
  2 + 3 is 5
  5 * 4 is 20
  20 + 5 is 25

No! it does not, even though the newcomer might think that was the most natural way for it to work.

Almost all programming languages use a system in which operators of some types are run first, then operators of different types. In our example above, it runs he multiplication before the additions, so
  3 * 4 is 12
  2 + 12 is 14
  14 + 4 is 19

And you see that's a very different result to the 25 if we had gone left to right. This really matters to all programmers!

There's a common acronymn that's used - BODMAS:

Brackets     .
Order / Index
Division
Multipication
Addition
Subtraction

• Anything that's in round brackets is run first (and that's very important, because it means you can add brackets to change the order of evaluation if you need to do so)

• Then orders / indexes are run. They are "raise to the power of" operations such as
  2 ** 7
for 2 to the power 8 - i.e. 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 which is 256

• Then divisions and multiplications (these are done at the same time, from left to right within your expression)
  16 / 4 * 2
will give the result 8 rather than 2, because the division, which is the same level as the multiplication, is to the left of the multiplication.

• Finally (in BODMAS), additions and subtractions are performed in the same "pass", again from left to right.

Precedence order may confuse the newcomer from time to time, but the heirarcy tree that's used has stood the text of time, and is sensible for real use, and pretty standard. There are many other operators you'll find yourself using in some of the languages we teach, and they typically slot in "naturally".


BODMAS is covered on all our "learning to program in " ... courses:
  Learning to program in PYTHON
  Learning to program in C
  Learning to program in Perl
  Learning to program in C++
  Learning to program in Ruby
  Learning to program in PHP
  Learning to program in Tcl
  Learning to program in Lua
If you're already an experienced programmer in another langauge, please see our full schedule as we run other courses which will help you convert without teaching you the basics you already know.
(written 2012-11-09, updated 2012-11-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y102 - Python - Fundamentals
  [328] Making programs easy for any user to start - (2005-05-29)
  [633] Copying a reference, or cloning - (2006-03-05)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [956] Python security - trouble with input - (2006-11-30)
  [1430] Integer v float - Python - (2007-11-12)
  [1448] Question on division (Java) - Also Perl, PHP, Python ... - (2007-11-28)
  [1461] Python - input v raw input - (2007-12-06)
  [1878] Pascals Triangle in Python and Java - (2008-11-10)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [3083] Python - fresh examples from recent courses - (2010-12-11)
  [3181] Beware - a=a+b and a+=b are different - Python - (2011-02-23)
  [3278] Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. - (2011-05-05)
  [3551] Some terms used in programming (Biased towards Python) - (2011-12-12)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [4324] Learning to program - variables and constants - (2014-11-22)
  [4442] Mutable v Immuatble objects in Python, and the implication - (2015-02-24)
  [4712] A reminder of the key issues to consider in moving from Python 2 to Python 3 - (2016-10-30)

U102 - Lua - Numbers and the Math library.
  [1699] If you are learning Lua, here are some more examples - (2008-07-06)
  [1744] Lua examples, Lua Courses - (2008-08-08)
  [2345] Automatically initialising Lua variables the first time - (2009-08-10)
  [2509] A life lesson from the accuracy of numbers in Excel and Lua - (2009-11-21)
  [4569] Lua - changes to how integers and floats are handled - 5.2 to 5.3 - (2015-11-02)

T202 - Tcl/Tk - Tcl Fundamentals
  [3] Looking for a donkey - (2004-08-05)
  [210] Joining lists in Tcl. Indirect variables in Tcl. - (2005-02-12)
  [349] Comments in Tcl - (2005-06-16)
  [362] The ireallyreallywanna operator - (2005-06-28)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [1426] Buffering up in Tcl - the empty coke can comparison - (2007-11-10)
  [1469] Curley brackets v double quotes - Tcl, Tk, Expect - (2007-12-12)
  [4453] Tcl variable names - no real limits! - (2015-03-10)

R103 - Basic Ruby Language Elements
  [986] puts - opposite of chomp in Ruby - (2006-12-15)
  [2287] Learning to program in Ruby - examples of the programming basics - (2009-07-15)
  [2296] Variable scope - what is it, and how does it Ruby? - (2009-07-18)
  [2613] Constants in Ruby - (2010-02-01)
  [2617] Comparing floating point numbers - a word of caution and a solution - (2010-02-01)
  [3430] Sigils - the characters on the start of variable names in Perl, Ruby and Fortran - (2011-09-10)
  [3758] Ruby - standard operators are overloaded. Perl - they are not - (2012-06-09)
  [4369] Ruby - the second rung of learning the language - (2014-12-28)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)

P202 - Perl Fundamentals
  [184] MTBF of coffee machines - (2005-01-20)
  [1312] Some one line Perl tips and techniques - (2007-08-21)
  [1726] Hot Courses - Perl - (2008-07-28)
  [1826] Perl - Subs, Chop v Chomp, => v , - (2008-10-08)
  [1946] Variable Types in Perl - (2008-12-15)
  [2832] Are you learning Perl? Some more examples for you! - (2010-06-27)
  [2876] Different perl examples - some corners I rarely explore - (2010-07-18)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [3102] AND and OR operators - what is the difference between logical and bitwise varieties? - (2010-12-24)
  [3329] Perl from basics - (2011-06-20)
  [3398] Perl - making best use of the flexibility, but also using good coding standards - (2011-08-19)
  [3542] What order are operations performed in, in a Perl expression? - (2011-12-07)
  [3574] Perl functions such as chop change their input parameters - (2012-01-10)

J703 - Java - Variables
  [127] Conversion and coercion in Java - (2004-11-22)
  [2148] Variable scope in Java Servlets and other web applications - (2009-05-01)
  [2153] Class Loading and Variable Conversion in Java - (2009-05-02)
  [3038] Setting up individual variables, and arrays, in Java - some commented examples - (2010-11-09)
  [3041] Java - basic rules for arithmetic, variables and conversion - (2010-11-10)
  [3365] Turning bright delegates into bright and knowledgable ones - (2011-07-21)
  [4345] Incrementing a variable in Java - Pre and Post Increment - (2014-12-08)

H103 - PHP - Variables, Operators and Expressions
  [483] Double Dollars in PHP - (2005-11-02)
  [2215] If nothing, make it nothing. - (2009-06-02)
  [3916] PHP variables - dynamically typed. What does that mean? - (2012-11-08)
  [4642] A small teaching program - demonstration of principles only - (2016-02-08)

C201 - C and C based languages - C Language Fundamentals
  [888] Turning C from source to a running program - (2006-10-06)
  [1671] Compiling C programs with gcc - an overview - (2008-06-10)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2576] What does const mean? C and C++ - (2010-01-15)
  [2842] Staring a C course with Hello World - why? - (2010-06-30)
  [3120] Learning to write good programs in C and C++ - separating out repeated code - (2011-01-04)
  [3234] Your program - you just provide the filling in the sandwich - (2011-04-08)
  [3591] Integer types, and integer overflows, in C - (2012-01-25)
  [4555] Preprocessor directives in C and C++ - what they mean - (2015-10-27)
  [4566] C - why is slow to write and debug) but fast to run? - (2015-11-01)


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Some other Articles
On rememberance, on war, and on preventing the war cycle
Challenge for a photographer
What is a web framework?
Multiple page web applications - maintaining state - PHP
BODMAS - the order a computer evaluates arithmetic expressions
How does PHP work?
While, for, foreach or something else to loop.
How many times ... has this loco headed west through Tenby? - Python exceptions
Sand to Arabia, Coals to Newcastle or Woodburners to Russia
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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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