Perl Loops & Decisions

Front 1

Give an example of declaring multiple variables.

Back 1

my ($a, %b, @c);
Note that the parentheses are required when declaring multiple variables on one line. due to the lower precedence of my to a ,.

Front 2

What does chomp() do?

Back 2

It removes all new lines if a string has one, otherwise it does nothing. It returns the number of newlines removed.

Front 3

What does the exists function do?

Back 3

It determines if a hash key exists.
exists $hash{$key;
returns 1 or 0

Front 4

What does the defined function do?

Back 4

It determines if a variable has a value.
defined $a;

Front 5

What does unless do?

Back 5

It is equivalent to - if not.

Front 6

What is a statement modifier?

Back 6

It has the form <action> if <condition>.
example:
die "Stupid mistake" unless exists $smart;

Front 7

How do you use "or" to execute a conditional action?

Back 7

exists $something or print "nothing";
Left side is evaluated first, and if it isn't true then the right hand side is evaluated.

Front 8

How do you use "and" to execute a conditional action?

Back 8

exists $something and print "something";
If left side and right side are true then it will execute right side.

Front 9

What is a good way to execute one of many different options without using if elseif?

Back 9

for ($branch){
$_ == 1 && print "1 \n";
$_ == 2 && print "2 'n";
...
}

Front 10

Are for and foreach equivalent?

Back 10

Yes.

Front 11

What is the difference between declaring the iterator variable outside the loop or in the loop.

Back 11

If it is outside the loop it will return to the value it had before the loop was executed after the loop completes. If inside it will only exist while the loop is iterated.

Front 12

What does "$total += $_ for @ARGV;" do?

Back 12

It sums up all the arguments from the input and assigns the value to the $total variable.

Front 13

How do you modify the while statement?

Back 13

<actions> while <condition>
print "something" while $countdown-- > 0;

Front 14

What does the until command do?

Back 14

It is the opposite of while meaning <not condition>

Front 15

What does the last statment do?

Back 15

It will break out of a loop if condition is true.
while(1){
last if 1;
}

Front 16

What does the next statement do?

Back 16

It stops executing the rest of the body instructions and begins a new loop iteration.

Front 17

What does the redo statement do?

Back 17

It reruns the body of the loop without iterating.

Front 18

What do loop labels allow you to do?

Back 18

You can give each loop a name and when you do a last you can exit out of the loop name in the last statement.