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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Comparing loop commands in Tcl

Tcl offers you three different loop commands - here they are generating the same output:

while A condition is tested, and if true the commands in a loop are performed. The condition is then retested (provided that you have passed the test into while as a deferred block)

  set month 1
  while {$month <= 12} {
    puts "2. This is for month $month"
    incr month
    }


for A prettified version of while - it takes two extra parameters which are normally used to initialise a variable, and to increment that variable before the test is redone.

  for {set month 1} {$month <= 12} {incr month} {
    puts "1. This is for month $month"
    }


foreach Run a block of code (a loop) for each value in a list.

  foreach month {1 2 3 4 5 6 7 8 9 10 11 12} {
    puts "3. This is for month $month"
    }


The latter is significantly different in its use and intent.

See full program [here].

All loops taught / covered / compared on our Tcl and Tcl/Tk courses.
(written 2012-01-06)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T203 - Tcl/Tk - Conditionals and Loops
  [210] Joining lists in Tcl. Indirect variables in Tcl. - (2005-02-12)
  [1401] Tcl - using [] or {} for conditions in an if (and while) - (2007-10-23)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [2261] Tcl - nice and nasty - (2009-06-29)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2681] Tcl - a great engineering language - (2010-03-17)
  [3189] Tcl - the danger of square brackets in a while command - (2011-03-02)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)


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Some other Articles
Multiple buttons calling the same proc in wish (tcl/tk)
Perl functions such as chop change their input parameters
New in Java 7 - and why we are not running public Java 7 courses
Adding Expect on top of Tcl - what is it and where can I get a training course to learn about it?
Comparing loop commands in Tcl
Images of the new year in Melksham
Telling which ServerAlias your visitor used - useful during merging domains
First of the year
Initial thoughts - response to GW Rail Franchise Consultation for Wiltshire
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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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