tcl newbie: can't count length of array

jimieee · 05-28-2006, 11:41 AM

Hi,

Can someone tell me why I can't count the number of elements in an array initialised like this:

Code:

set counter 0
set input 0
while {$input != "."} {
    gets stdin input
	if {$input != "."} {
	    set array1($counter) $input
    }
	set counter [expr $counter + 1]
}
set array1_length [llength $array2]
puts "array1 has $array1_length records"

But I can when I initialise it like this?:

Code:

set working_array {1 2 3 4 5 6}
set working_array_count [llength $working_array]
puts $working_array_count

Many Thanks,

James

exvor · 05-28-2006, 03:39 PM

Im not sure what programming lanugae this is but in C i know that an array is a set length that when compiled the compiler will create memory allocation for the set size. Stdin is a buffer for imput from the keyboard and thus has a varible lengh. So when trying to compile the compiler doesent know how much memory to set for the array. so it gives you an error.

Mabye wrong if your doing perl or java as the code isent compiled.

jlinkels · 05-28-2006, 03:49 PM

I think because llength is an operator which operates on sets, and not on arrays.

In your second example you assign a number of elements to a set. Hence llength returns the number of elements in the set.

On the first example you have an array. If you want to know the number of elements there, you should use array size arrayname

I take it [llength array2] is a typo?

jlinkels

jimieee · 05-30-2006, 07:17 AM

>> Im not sure what programming lanugae this

It's tcl. See the subject line of my first post

>> I think because llength is an operator which operates on sets, and not on arrays.

Yeah, I think you're onto something here. Frustratingly enough this is the error message I get:

Code:

can't read "array1": variable is array

Nice huh?

Wim Sturkenboom · 05-30-2006, 07:42 AM

Code:

puts [array size array1]

or something similar should do.

See man n array

jimieee · 05-31-2006, 03:35 PM

Ah! There's something I wasn't quite aware of here:

"Tcl supports an object not found in most programming languages: the list"

It turns out that a list and an array are two different things as far as Tcl is concerned. llength is short for "list length", so it doesn't work on arrays.

From what I understood from here the main difference between a list and an array (in Tcl) is that whilst an array is an indexed set of values (it behaves similarly to a hash in Perl) a list is just a string that's divided up with seperators.

Lists provide a convienient, though not very efficient, way to store and manipulate data.

Am I correct?

jlinkels · 05-31-2006, 05:56 PM

Oh but you can extract the n-th item from a list equally well :-)

I don't know what the internal implementation of lists and arrays etc is.

Did you dowload and take the tcl tutor?

I found it very valuable, as I think tcl has an extremely steep learning curve. Just the kind of problem you struggled with... and tcl is full of them. Nevertheless, it is a great and powerful language.

jlinkels

jimieee · 06-01-2006, 06:41 AM

No, I didn't find that one. Thanks

I've been learning from (quite an old) book. I need to know a bit about it for work, but you're right it does look like a very powerful language.

bigearsbilly · 06-01-2006, 08:29 AM

woops double posted

bigearsbilly · 06-01-2006, 08:29 AM

well, anyway for a start you are getting the length of array1
and printing the length of array2 !!!!!

Code:

set counter 0
set input 0
while {$input != "."} {
    gets stdin input
	if {$input != "."} {
	    set array1($counter) $input
    }
	set counter [expr $counter + 1]
}
set array1_length [llength $array2]
puts "array1 has $array1_length records"

and it's array size array1

have you got tkcon?
it's good for playing about.
and tclhelp is good too

bigearsbilly · 06-01-2006, 08:42 AM

also it's inc counter

jimieee · 06-02-2006, 05:59 AM

Yeah, basically being a newbie I'm a bit of an ignoranus

I realised that error after my first post and corrected it, but still had the problem with lists not being the same thing as arrays

Still these are good tips!

For reference I was just doing this so that I could practise make lists, merging them, sorting them, that sort of thing. This is what I ended up doing:

Code:

#!/usr/bin/tclsh
# Print the date 
puts [exec date +%d/%m/%Y\ %H:M\n]
# Short explanation of what the program does
puts "This program takes two lists from standard input, joins them, sorts them and splits them again\n"
# Get the first list
puts "Please start entering values for the first list. Finish entering a . to finish: "
set input 0
set list1 { }
while {$input != "."} {
    gets stdin input
	if {$input != "."} {
	    lappend list1 $input
	}
}
# Get the second list
puts "Please start entering values for the second list. Finish entering a . to finish: "
set input 0
set list2 { }
while {$input != "."} {
    gets stdin input
	if {$input != "."} {
	    lappend list2 $input
	}
}
# Get the length of the lists
set list1_length [llength $list1]
set list2_length [llength $list2]
puts "list 1 has $list1_length records"
puts "list 2 has $list2_length records"
# Join the lists
set superlist [concat $list1 $list2]
# Print list
puts "The joined list contains:"
puts $superlist
# Sort the lists
set superlist [lsort -integer $superlist]
# Print the list
puts "This is the list after it's been sorted:"
puts $superlist
# Split the lists into their original lengths
# Blank the list
set list1 { }
set count 0
while {$count < $list1_length} {
   lappend list1 [lindex $superlist $count]
   set count [expr $count + 1]
}
# Blank the list
set list2 { }
while {$count < [expr $list1_length + $list2_length]} {
   lappend list2 [lindex $superlist $count]
   set count [expr $count + 1]
}
# Print both lists seperately
puts "The new contents of list 1:"
puts $list1
puts "The new contents of list 2:"
puts $list2

It's not quite perfect, but I'll have another go and add in the suggested improvements sometime over the weekend.

Thanks

exvor · 06-03-2006, 12:38 PM

Quote:

Originally Posted by jimieee

>> Im not sure what programming lanugae this

It's tcl. See the subject line of my first post

Ahh I dident know TCL was a language. I always thought it was just a library.