How can you iterate an array? And a hash?

• Array:

my @numbers = qw/1 2 3 4 5/;

# Using `$_` that represents the current iteration in a loop. It starts from index array 0 until the last index.
foreach (@numbers) {
    print($_);
}
# Output: 12345

# "$#" returns the max index of an array. That's the reason because we can iterate accessing to the array from the index 0 to the max index.
for my $i (0..$#numbers) {
    print($numbers[$i]);
}
# Output: 12345

# Using the `map` keyword:
print map {$_} @numbers;
# Output: 12345

# Using `while`. We should take care with this option. When we use `shift` we're deleting the first element of the array and assigning it to the `element` variable.
# After this `loop` the `numbers` array will not have elements.
while (my $element = shift(@numbers)) {
    print($element);
}
# Output: 12345

• Hashes:

my %capital_cities = (
 'Madrid' => 'Spain',
 'Rome' => 'Italy',
 'Berlin' => 'Germany'
);

# Iterate and get the `keys`:
foreach my $city (keys %capital_cities) {
   print($city . "\n");
}
# Iterate and get the `values`:
foreach my $country (values %capital_cities) {
   print($country . "\n");
}

# Iterate and get the values and keys (first option):
foreach my $city (keys %capital_cities) {
   print("City: $city - Country: $capital_cities{$city}" . "\n");
}

# Iterate and get the values and keys (first option):
while(my ($city, $country) = each %capital_cities) {
   print("City: $city - Country: $capital_cities{$city}" . "\n");
}