#!/usr/bin/perl -w 
use strict;
 my @primes = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47);

sub listprimes {
 my $n = shift; 
my $i = 0;
 my $answer = "";

 while ($primes[$i]<=$n) {
 $answer .= " $primes[$i]"; 
$i++; } return $answer;
 } 

sub random { 
my($a,$b) = @_;
 return int(rand($b-$a+1))+$a;
 }

 my $a = random(10,50); 
my $f = listprimes($a); print "$f\n";
[download]

When I run this code, it will pickup the random number. I do not understand the code much, can explain for me. And hint for me if I want to rewrite the code which use the foreach and push funtion

Update

#!/usr/bin/perl -w 
use strict;
 my @primes = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47);

sub listprimes {
 my $n = shift; 

 my @answer = ();

 

 foreach $a(@prime) {
  if($a<=$n){push @answer,$a;}

 return @answer;
}


sub random { 
my($a,$b) = @_;
 return int(rand($b-$a+1))+$a;
 }

 my $a = random(10,50); 
my $f = listprimes($a); print "$f\n";
[download]

I rewrite this program by using the foreach and push function. But it is not run, please help me to fix it

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