if 0 {
<<TOC>>
----

**Introduction**
[MiHa] 2015-06-13: 
HelloWorld-programs are supposed to be the most simple, working programs of a given language.

But I want to extend such a HelloWorld-program to a one-page - reference-card, <<br>>
where all the essential features of the language are shown. <<br>>
Several short programs would be ok, too. <<br>>
If possible, while doing something useful (and/or funny).

Tcl by itself (without Tk) is http://wiki.tcl.tk/10259%|%quite simple%|%, 
so an amount of code to fill about one printed page should be enough. <<br>>
(The layout may need to be tweaked, e.g. printing front and back, landscape, and in 2-4 columns:)

Basic [Tcl Commands] to cover:
   * http://wiki.tcl.tk/1669%|%Comments%|% / statements
   * Output: [puts] / -nonewline
   ** [format]
   * Numeric [variable]s: [set]
   * multiple statements / assignments in one line
   ** simple calculations: [incr] / [expr]
   * [proc] / [return] - for functions
   * basic flowcontrol:
   ** [if] / then / else / elseif / comparing
   ** [for] - loop,  maybe also the [while]-loop / [break] / [continue]
   * [foreach]
   * String variables / quoting 
   * [exit]

Advanced features (to include if space permits):
   * input: [gets], [eof], [scan] / checking the input <<br>>This is an important topic, but likely too much for one page.
   * [catch]
   * [global] / $::var
   * [string]-operations (e.g. find/extract/replace char in a string, append, delete/split ...)
   * [data structure]s: 
   ** [array] / [parray]
   ** [list] / [lassign], [lappend], [lset], [linsert], [lreplace] / [lindex], [llength] / [lrange], [lsearch], [lsort]
   ** [dict]
   * [file]-operations / [open], [close ] / [glob]

...

More features, to be left out, for a later lesson (too advanced, or too rarely needed for an introduction):
   * [upvar] / [uplevel]
   * [namespace]s
   * [eval]
   * [interp]
   * [lambda]
   * [regexp] - this is very likely too complex to cover as just one small example on a general introduction page.
   * [switch]
   * [unknown]
...

Things to be aware of:
   * comments are commands, so quotes and braces inside need to be balanced
   * when to use / not to use "$" with variablenames ( set i 1; puts $i; incr i $i )

Maybe there already are some programs here in the wiki 
that would qualify for such a refcard-program...

}
----
**Program 1 - puts**
======tcl
  # HelloWorld001.tcl - 2015-06-13 - http://wiki.tcl.tk/41268

  # Output a string to terminal:

  puts "Hello, World!"

  ### END ###
======

----
**Program 2 - set, incr**
======tcl
# HelloWorld002 - 2015-06-23
# http://ideone.com/9KlN4c

# Assign value to variables, and output:

set a "The answer is"
set n 42

puts $a
puts $n

incr n                ;# add 1 to a numeric variable
puts "$a now $n"

# END #
======
***Output 2***
======none
The answer is
42
The answer is now 43
======

----

**Program 3 - clock, timedate, if, else**
======tcl
# HelloWorld003.tcl - MiHa - 2015-06-13
# http://wiki.tcl.tk/41268 / http://ideone.com/xl0IBI

# Query the time (cs as a number, td and hh as a string), 
# output depending on the value of the hour:

set cs [clock seconds]                                    ;# seconds since 1970-01-01
set td [clock format $cs  -format "%Y-%m-%d  %H:%M:%S" ]  ;# timedate
set hh [clock format $cs  -format %H ]                    ;# hours (00-23)

puts "cs=$cs  td='$td'  hh=$hh"

if { $hh < "12" } {
    puts -nonewline "Good morning, "
} else {
    puts -nonewline "Hello, "
}
puts "World!"

# END #
======
***Output 3***
======none
cs=1434926575  td='2015-06-21  22:42:55'  hh=22
Hello, World!
======

----
**Program 4 - clock, if,elseif**
======tcl
# HelloWorld004.tcl - MiHa - 2015-06-21
# http://wiki.tcl.tk/41268 / http://ideone.com/Llp8Os

# Query the hour from the clock, 
# output text depending on the value of the hour:

set cs [clock seconds]                          ;# seconds since 1970-01-01
set hh [clock format $cs  -format %H ]          ;# hours (00-23)

puts "cs=$cs  hh=$hh"

if { $hh < "12" } {
    puts -nonewline "Good morning, "
} elseif { $hh > "18" } {
    puts -nonewline "Good evening, "
} else {
    puts -nonewline "Hello, "
}
puts "World!"

# END #
======

***Output 4***
======none
cs=973531773  hh=17
Hello, World!
======
and
======none
cs=1434927642  hh=23
Good evening, World!
======

----
**Program 5 - string compare**
======tcl
# HelloWorld005 - 2015-06-23
# http://ideone.com/OJoort

# Comparing strings:

set hh "20"

set tx "Hello"
if { $hh < "12" } { set tx "Good Morning" }
if { $hh > "18" } { set tx "Good Evening" }

puts "It is $hh:00 --> $tx, World !"
#.
======

***Output 5***
======none
It is 20:00 --> Good Evening, World !
======

----
**Program 6 - proc**
======tcl
# HelloWorld006 - 2015-06-23
# http://ideone.com/GBiMab

# Comparing strings, proc as function

proc greeting {hh}  {
  set gr "Hello"
  if { $hh <  "12" } { set gr "Good Morning"    }
  if { $hh == "12" } { set gr "Happy Lunchtime" }
  if { $hh  > "18" } { set gr "Good Evening"    }
  return $gr
}

set hh "12"
set tx [greeting $hh]
puts "It is $hh:00 --> $tx, World !"

#.
======

***Output 6***
======none
It is 12:00 --> Happy Lunchtime, World !
======

----
**Program 7 - while, gets**
======tcl
# HelloWorld007 - 2015-06-23
# http://ideone.com/mcV6YL

# Comparing strings, proc as function, input in while-loop

proc greeting {hh}  {
# This proc returns a result as soon as a match is found:
  set gr "Hello"
  if { $hh <  "12" } { return "Good Morning"    }
  if { $hh == "12" } { return "Happy Lunchtime" }
  if { $hh  > "24" } { return "Goodbye" }
  if { $hh  > "18" } { return "Good Evening"    }
  return $gr
}

set hour "99"               ;# start with any value that keeps the loop going
while { $hour > "0" } {
  puts -nonewline "Enter hour, 0 to quit: "
  set hour [gets stdin]
  puts $hour
  
  puts "It is $hour:00 --> [greeting $hour], World !"
}
puts "Bye!"

#.
======

***Output 7***
======none
Enter hour, 0 to quit: 1
It is 1:00 --> Good Morning, World !
Enter hour, 0 to quit: 11
It is 11:00 --> Good Morning, World !
Enter hour, 0 to quit: 12
It is 12:00 --> Happy Lunchtime, World !
Enter hour, 0 to quit: 15
It is 15:00 --> Hello, World !
Enter hour, 0 to quit: 17
It is 17:00 --> Hello, World !
Enter hour, 0 to quit: 18
It is 18:00 --> Hello, World !
Enter hour, 0 to quit: 19
It is 19:00 --> Good Evening, World !
Enter hour, 0 to quit: 25
It is 25:00 --> Goodbye, World !
Enter hour, 0 to quit: 0
It is 0:00 --> Good Morning, World !
Bye!
======

----
**Program 8 - for, format**
======tcl
# HelloWorld008 - 2015-06-23
# http://ideone.com/lKo08L

# Comparing strings, proc as function, for-loop, format

proc greeting {hh}  {
# This proc returns a result as soon as a match is found:
  set gr "Hello"
  if { $hh <  "12" } { return "Good Morning"    }
  if { $hh == "12" } { return "Happy Lunchtime" }
  if { $hh  > "24" } { return "Goodbye" }
  if { $hh  > "18" } { return "Good Evening"    }
  return $gr
}

puts "Greeting:"
for {set h 0} {$h<=25} {incr h} {
 #set hour $h                  ;# Tcl converts number to string, as needed
 #set hour [format "%2d"  $h]  ;# format as numeric string with 2 digits
  set hour [format "%02d" $h]  ;# format as 2 digits with leading 0
  puts "at $hour:00 --> [greeting $hour], World !"
}
puts "Done."

#.
======

***Output 8***
======none
Greeting:
at 00:00 --> Good Morning, World !
at 01:00 --> Good Morning, World !
at 02:00 --> Good Morning, World !
at 03:00 --> Good Morning, World !
at 04:00 --> Good Morning, World !
at 05:00 --> Good Morning, World !
at 06:00 --> Good Morning, World !
at 07:00 --> Good Morning, World !
at 08:00 --> Good Morning, World !
at 09:00 --> Good Morning, World !
at 10:00 --> Good Morning, World !
at 11:00 --> Good Morning, World !
at 12:00 --> Happy Lunchtime, World !
at 13:00 --> Hello, World !
at 14:00 --> Hello, World !
at 15:00 --> Hello, World !
at 16:00 --> Hello, World !
at 17:00 --> Hello, World !
at 18:00 --> Hello, World !
at 19:00 --> Good Evening, World !
at 20:00 --> Good Evening, World !
at 21:00 --> Good Evening, World !
at 22:00 --> Good Evening, World !
at 23:00 --> Good Evening, World !
at 24:00 --> Good Evening, World !
at 25:00 --> Goodbye, World !
Done.
======

----
**Program 9 - expr, format**
======tcl
# HelloWorld00x.tcl - 2015-06-xx

#.
======

***Output 9***
======none
xx
======
----


Some ideas:
   * Table of primes
   * Dice-rolling
   ** with min/max/average
   * Calculate distance
   * Number of days between dates
...




----
 **Program x**
======tcl
# HelloWorld00x.tcl - 2015-06-xx

#.
======

 ***Output x***
======none
xx
======
----


----
**Remarks**
This is the Alpha-version, there ''will'' be bugs,
so use with caution <<br>>
...

----
'''See also:'''
   * http://wiki.tcl.tk/41210%|%ClockDemo%|%
   * ...

   
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