1 #!/usr/bin/perl -w
  2 
  3 use strict;
  4 
  5 my %course = (
  6         2 => 'c',
  7         1 => 'unix',
  8         3 => 'shell',
  9         4 => 'perl',
 10 );
 11 
 12 while (  (my $key, my $value) = each(%course) ) {
 13         print "$key => $value\n";
 14     }
 15 
 16         print "\nSorted values of hash:\n";
 17 foreach  my $val (sort values %course){
 18         print "$val\n";
 19 }
 20 print "\nEnter Key: ";
 21 my  $type = <stdin>;
 22 print  "you will be taking $course{$type} this semester\n";

##</code><code>##

:~/pbe/chap5$ ./exer5.pl 
4 => perl
1 => unix
3 => shell
2 => c

Sorted values of hash:
c
perl
shell
unix

Enter Key: 2
Use of uninitialized value within %course in concatenation (.) or string at ./exer5.pl line 22, <stdin> line 1.
you will be taking  this semester