if/elsif/else and switch statemements

For more complicated decision trees, the use of an if(){} elsif(){} else{} block may be needed:

my $age = 22;
if ($age < 13) {
  print "You aren't old enough to be a teenager";
}
elsif ($age < 20) {
  print "You are a teenager";
}
else {
  print "You're too old to be a teenager";
}

Multiple elsif statements may be used within this block. If there are many possibilities to handle, it may be more readable to use a type of SWITCH statement - one example is as follows:

my $age = 22;
SWITCH: {
  ($age < 13) and do {
      print "You're too young to be a teenager";
      last SWITCH;
  };
  ($age < 20) and do {
      print "You're a teenager";
      last SWITCH;
  };
  print "You're too old to be a teenager";
}

Here, we use a named block (in this example, called SWITCH), in which various conditions are tested for. If one is met, the statements within the following do{} block are executed - note the use of the last SWITCH statement to force termination of the rest of the block. The last statement within the block is a default, which will be executed if none of the previous conditions are met.

As for loops, it is possible to next if/elsif/else blocks inside of each other. Again as for loops, it is very good practice to get into the habit of indenting things. The following code

my $i = 3;
my $j = 12;
my $k = 0;
if ($i < 30) {
  if ($j > 32) {
    $k = 22;
  }
  else {
    $k = 98;
  }
else {
  $k = 321;
}

is much easier to read and to follow the logic of than

my $i = 3;
my $j = 12;
my $k;
if ($i < 30) {
if ($j > 32) {
$k = 22;
}
else {
$k = 98;
}
else {
$k = 321;
}

or even

my $i = 3;
my $j = 12;
my $k;
if ($i < 30) { if ($j > 32) { $k = 
22; } else { $k = 98; } else { $k = 321;}

even though all three examples will mean the same to Perl.