#    if (Expression) {Code Segment}
#    if (Expression) {Code Segment} else {Code Segment}
#    if (Expression) {Code Segment} elsif {Code Segment} ... else {Code Segment}

    #!/usr/local/bin/perl -w

    while (<STDIN>)
    {
       chomp;

       if ($_ < 10)
       {
          print "$_ is less than 10.\n";
       }
       elsif ($_ < 20)
       {
          print "$_ is between the values of 10 and 19.\n";
       }
       else
       {
          print "$_ is greater than or equal to 20.\n";
       }
    }