Control Structures

Summary

if

if (expression) {         # condition
   __________________;
   __________________;
   
} elsif (expression) {
   __________________;
   __________________;
   
} elsif (expression) {
   __________________;
   __________________;
   
} else {
   __________________;
   __________________;
} 

unless

unless (expression) {     # condition
   __________________;
   __________________;    # do if false
   __________________;
   
} else {
   __________________;
   __________________;    # do if true
   __________________;
}

while

while (expression) {    # condition
   __________________;
   __________________;  # do if expression is true
   __________________;  # then go back and recheck expression
   
}

until

until (expression) {    # condition
   __________________;
   __________________;  # do if expression is false
   __________________;  # then go back and recheck expression
   
}

foreach

foreach $i (@some_array) {
   __________________;
   __________________;      # iterate over array elements
   __________________;
}

foreach (1 .. $n) {
   __________________;
   __________________;      # repeat $n times
   __________________;
}

for

Example: print all even numbers between 4 and 12:

for ($i = 4; $i <= 12; $i += 2) {
   print "$i\n";
}

my $i = 4;           # set initial state of $i

while ($i <= 12) {   # condition to test $i
   print "$i\n";
   $i += 2           # modify $i
}

Comparison operators

What is true?

1. Any string except for "" and "0".
2. Any number except for 0.
3. Any non-empty array.