Read coordinates

[Berk Birand]

Hi,

I am new to Perl (as a matter of fact, I started learning it a couple of
days ago; I have some previous programming experience though). When
looking for the ideal languages to use for a particular project, I came
across perl, and starting writing the script.

I need to read a text containing some coordinates:
248,156
322,156
326,368
248,368

326,194
950,194
960,360
326,364

....

I need to process these coordinates and find the center of gravity of the
structure.

For now I have this code.

#! /usr/bin/env perl

open(HELL,"plc") or die "Can't open plc: $!";
my @x;
my @y;

#first read the file
#put the coordinates in special variables

while (<HELL>) { # assigns each line in turn to $_
$_ =~ /(\d+),(\d+)/;

for($i=0; $i<=3;$i++) {
@x[$i] = [ $1 ] ;
@y[$i] = [ $2 ];

print $x[1]; }

# print "the x is $1 \n";
# print "the y is $2 \n";
# print "Just read in this line: $_";

# do the necessary calculations
# [...]
}
I thought about putting each coordinate in an array of x and y values, and
then finding their arithmetic means.
However I do not know how to augment the arrays size at each iteration of
while. The size of the array cannot be changed can it?
Help would be greatly appreciated!

Thanks

BB

[Jürgen Exner]

Berk Birand wrote:
[...]

However I do not know how to augment the arrays size at each
iteration of while. The size of the array cannot be changed can it?

I think you are looking for the push() function, see "perldoc -f push"

jue

[Berk Birand]

On Sun, 07 Mar 2004 00:25:49 +0000, Jürgen Exner wrote:

I think you are looking for the push() function, see "perldoc -f push"

Yes, that solved the problem quite well.
Thanks Jürgen.

[Jim Gibson]

In article <41******************************@news.teranews.co m>, Berk
Birand <gr************@NOSPAMyahoo.com> wrote:

Hi,

I am new to Perl (as a matter of fact, I started learning it a couple of
days ago; I have some previous programming experience though). When
looking for the ideal languages to use for a particular project, I came
across perl, and starting writing the script.

I need to read a text containing some coordinates:
248,156
322,156
326,368
248,368

326,194
950,194
960,360
326,364

...

I need to process these coordinates and find the center of gravity of the
structure.

For now I have this code.

#! /usr/bin/env perl

You should let Perl help you while you are developing code:

use strict;
use warnings;
open(HELL,"plc") or die "Can't open plc: $!";
my @x;
my @y;

#first read the file
#put the coordinates in special variables

my $i = 0; #(see below)
while (<HELL>) { # assigns each line in turn to $_
$_ =~ /(\d+),(\d+)/;
Always check to see if the match worked before using the results:

if( /(\d+), (\d+)/ ) {
for($i=0; $i<=3;$i++) {
Why are you assigning the extracted coordinates 4 times?
@x[$i] = [ $1 ] ;
This is assigning a reference to an array of one element ( [ $1 ] ) to
an array slice of one element ( @x[$i] ). This is not likely to be what
you want. @y[$i] = [ $2 ];
Maybe you want just:

$x[$i] = $1;
$y[$i] = $2;
$i++;

where you refer to the n'th element of @x as $x[n]. If so, then you
need the declaration of $i above, before and outside the loop.

print $x[1]; }

# print "the x is $1 \n";
# print "the y is $2 \n";
# print "Just read in this line: $_";

# do the necessary calculations
# [...]
}
Now you can do a calculation with the contents of @x and @y:

for my $i ( 0 .. $#x ) {
print "$x[$i], $y[$i]\n";
}
I thought about putting each coordinate in an array of x and y values, and
then finding their arithmetic means.
However I do not know how to augment the arrays size at each iteration of
while. The size of the array cannot be changed can it?
Help would be greatly appreciated!

Thanks

BB