Perl Circle Array Function - arrays

Question

I am searching for help on how to loop through an array. I have source code that takes a number for a radius of a circle and produces its circumference. This only takes one number, and I would like to get multiple circumferences.
#!/usr/bin/env perl
use warnings;
$pi = 3.141592654;
print "What's the radius? ";
chomp($radius = <STDIN>);
$circle = 2 * $pi * $radius;
if ($radius < 0 ) {
$circle = 0;
}
print "The circumference of a circle with the radius of $radius is $circle.\n";
Now I want to be able to input several numbers for multiple radii using a while loop to put them into an array. Once I enter 0 or a number less than 0 the while loop will exit and the program will continue by looping through the array of user entered numbers and calculate the circumference of each circle using those values as a radii.
I have some code that is trying to do this, but I cannot seem to get it to work.
#number = <STDIN>;
while(<>) {
print "whats the radius? ";
my($circle, $radius, $pi);
$radius = &rad(<STDIN>);
$pi = 3.141592654;
$circle = 2 * $pi * $radius;
if ($radius <= 0){
return $circle; }
}
Any direction of where to go, or a simple solution would be greatly appreciated.

Answer 1

To do that with an array, you need to first read until you get a zero and push. Then you can process the array using a for or foreach loop. Those two are the same, but the syntax commonly associated with foreach is more perlish.
use strict;
use warnings;
# turn on autoflush so stuff gets printed immediately
$|++;
print "Please enter a bunch of numbers, or 0 to stop. ";
my #numbers;
while ( my $n = <> ) {
chomp $n;
# stop at zero or less
last if $n <= 0;
# store the number in the array
push #numbers, $n;
}
my $pi = 3.141592654;
foreach my $radius (#numbers) {
my $circumference = 2 * $pi * $radius;
# print with format (%s gets replaced by params)
printf "The circumference of a circle with radius %s is %s\n", $radius, $circumference;
}
Here's the input/output.
Please enter a bunch of numbers, or 0 to stop. 1
2
3
0
The circumference of a circle with radius '1' is '6.283185308'
The circumference of a circle with radius '2' is '12.566370616'
The circumference of a circle with radius '3' is '18.849555924'
When running your first program, I noticed that the What's the radius? message showed up under the input prompt. That is because your output buffer only gets flushed when you have a newline \n in the output (or in some other cases, but let's ignore those). To change that behaviour, you can enable autoflush on the buffer, or simply set $| to a value larger than zero. The increment-idiom is common to do that.
You can also use the Math::Trig module to get π. It comes with Perl and has a constant that gives you pi. Since constants in Perl are just subs, you import it like any other function from a module.
use strict;
use warnings;
use Math::Trig 'pi'; # load module and import the 'pi' constant
# ...
foreach my $radius (#numbers) {
my $circumference = 2 * pi * $radius;
# print with format (%s gets replaced by params)
printf "The circumference of a circle with radius %s is %s\n", $radius, $circumference;
}

Answer 2

use strict;
use warnings;
use Data::Dumper;
This repeats your code in a infinite loop, exiting if the radius <= 0.
It stores all corresponding values for circle and radius in arrays:
my (#circle, #radius);
while(1){
print "What's the radius? ";
chomp($radius = <STDIN>);
$circle = 2 * $pi * $radius;
print "The circumference of a circle with the radius of $radius is $circle.\n";
last if $radius <= 0;
push #circle, $circle;
push #radius, $radius;
}
print Dumper \#circle, \#radius;

Answer 3

Easier than it might sound - tone of the key ways of interacting with an array is via a for (or foreach - they're the same) loop. Each iteration of the loop, a variable is set to the iterator - you can specify it (I have below) but if you don't it uses $_ by default.
#!/usr/bin/perl
use strict;
use warnings;
my $PI = 3.141592654;
print "Please enter radii, terminate with ^D\n";
my #list_of_values = <STDIN>;
chomp ( #list_of_values ); #remove linefeeds
foreach my $radius ( #list_of_values ) {
print "Circumference of radius $radius is: ", $PI * $radius * 2,"\n";
}
The other trick I use above - is reading STDIN. Perl knows the difference between reading a single value - into a scalar - or reading a sequence of values into an array.
So it'll behave differently if you:
my $value = <STDIN>; #reads one line
my #values = <STDIN>; #reads all the lines
You could also do this with:
#!/usr/bin/perl
use strict;
use warnings;
my $PI = 3.141592654;
my #list_of_values;
print "Enter radii, or \"done\" if complete\n";
while ( my $input = <STDIN> ) {
chomp($input);
last if $input eq "done";
if ( $input =~ m/^[\d\.]+$/ ) {
push( #list_of_values, $input );
}
else {
print "Input of \"$input\" is invalid, please try again\n";
}
}
foreach my $radius (#list_of_values) {
print "Circumference of radius $radius is: ", $PI * $radius * 2, "\n";
}
for and foreach do the same thing, it's a matter of style which you use.