Version 17 of HelloWorld

if 0 {

• Introduction
• Program 1
• Program 2
• Output 2
• Program 3
• Output 3
• Program 4
• Output 4
• Remarks

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,
where all the essential features of the language are shown.
Several short programs would be ok, too.
If possible, while doing something useful (and/or funny).

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

Basic Tcl Commands to cover:

• Comments / statements
• Output: puts / -nonewline
  • format
• Numeric variables: 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
  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 structures:
  • 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
• namespaces
• 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

  # HelloWorld001.tcl - 2015-06-13 - http://wiki.tcl.tk/41268

  # Output a string to terminal:

  puts "Hello, World!"

  ### END ###

Program 2

# 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

The answer is
42
The answer is now 43

Program 3

# 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

cs=1434926575  td='2015-06-21  22:42:55'  hh=22
Hello, World!

Program 4

# 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

cs=973531773  hh=17
Hello, World!

and

cs=1434927642  hh=23
Good evening, World!

Some ideas:

• Table of primes
• Dice-rolling
  • with min/max/average
• Calculate distance
• Number of days between dates

...

Remarks

This is the Alpha-version, there will be bugs, so use with caution
...

See also:

• ClockDemo
• ...