print "\nAsking user which he/she taking: ";
my $choice = <STDIN>; chomp($choice);
if (exists $elective{$choice} ) {
    print "You will be taking the $elective{$choice} prog course\n";
                  }
                  else
                  {
                  print "No course taken\n";
                  }
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When you evaluate an array in scalar context (@k == <stdin>), you'll get the number of its elements, i.e. 4 in this case.