Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
 
Python and Tcl - public course schedule [here]
Private courses on your site - see [here]
Please ask about maintenance training for Perl, PHP, Lua, etc
 
Defining, declaring and initialising variables in C

When you declare a variable in C, you're instructing the compiler to set memory aside for it, and you're also telling the compiler how to handle any references to that memory.

• C does NOT spend time working out what sort of data you're storing and how many bytes are needed - it's up to you to tell it the right data sort and to make sure you handle it in the right way (though some checks and warnings are made for you at compile time)
• C does NOT spend time setting initial values into all the variables that you declare - it's up to you to initialise variables if it's needed within your application.

If you get these things wrong, you'll end up treating the bit pattern of an integer as if it's a float, or making use of whatever happened to be left in my ory from the last program during the running of your program, with results which will be unpredictable.

Example ([full source]) - with declarations without initialisation, I may get:

  int fred;
  float boat;


  munchkin:c12 grahamellis$ ./vars
  Integer is 32767; float is 27679303629726023680.000000
  munchkin:c12 grahamellis$


But with declarations with initialisations from the same program ([full source]) , I will get:

  int fred = 15;
  float boat = 17.778;


  munchkin:c12 grahamellis$ ./vars2
  Integer is 15; float is 17.778000
  munchkin:c12 grahamellis$


It is features like this, of C that make it a very fast language to run, but a very much longer-winded language in which to design and write code as there's so much more work you have to do to make sure things that other languages would check don't get overlooked. Just one of the reasons that C is great for the really heavy compute jobs, and for code that's copied millions of times like operating systems, but is a poor choice for lighter work and occasional code!

(written 2012-01-24, updated 2012-01-28)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C202 - C and C based languages - A first practical program
  [4632] Remember to ask the question before you listen for the answer - (2016-01-26)
  [4337] Learning to program sample program - past its prime, but still useful - (2014-12-02)
  [3236] C - a first program that does something useful for you - (2011-04-09)
  [3121] New year, new C Course - (2011-01-05)
  [2580] C course inspires new teaching examples - (2010-01-16)
  [888] Turning C from source to a running program - (2006-10-06)


Back to
Promoting a single one of your domains on the search engines
Previous and next
or
Horse's mouth home
Forward to
Integer types, and integer overflows, in C
Some other Articles
Back to Uni
Chars, char arrays and strings in C. Some early cautions and pitfalls.
Are we one man, one vote? No, and we never have been.
Integer types, and integer overflows, in C
Defining, declaring and initialising variables in C
Promoting a single one of your domains on the search engines
Learning about how to help people learning - and retaining
C++ Courses - do I get official certification at the end of my Well House course?
Emergency First Aid Provision at Well House Manor - part of the service
The changing Hotel and Bed and Breakfast business in Melksham
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page


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.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2019: 404 The Spa • Melksham, Wiltshire • United Kingdom • SN12 6QL
PH: 01225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/3590_Def ... -in-C.html • PAGE BUILT: Sat May 27 16:49:10 2017 • BUILD SYSTEM: WomanWithCat