1. Control Structures: for & while Loops
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2. Review Conditional Expression is a key component of Control Structures
The “value” of the conditional expression determines the program flow
Syntax: KEYWORD (expression) { statements }
e.g. if ($count<5) { print “count is $count\n”; }
Evaluation of Conditional Expression
True if the value of the expression is non-zero.
False if the value of the expression is zero (or null).
Comparison Operators (CO)  Compares two things
Numeric CO: ==, !=, >, >=, <, <=
String CO: eq, ne, gt, ge, lt, le
Logical Operators  Tests for multiple conditions
AND (&&), OR (II), NOT (!)
if Conditional Syntax
if (condexpr1) { statements1 } elsif (condexpr2) { statements2 }
else { statements3 }
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3. while Loop Syntax initialization Typically involves
while (exit condition) { statements }
Typically involves
variable initialization before the loop
exit condition
variable manipulation inside the loop to trigger loop exit
$a=“”; while ($a ne “x”) { $a=<STDIN>; chomp $a; print “$a\n”; }  Example script
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4. for Loop Iterative Loops are another type of control structures
statements are executed fixed number of times
Iterative Loops in Perl
for (initialization; test condition; increment) { statements } e.g. for ($i=1; $i<=5; $i++) { print “$i\n”; }
 Example script
foreach localvar(list expression) { statements }
list expression is an array variable or list
localvar is a scalar variable defined only for the duration of foreach loop
localvar holds list elements in sequential order
iterates through list elements e.g. foreach $i (1, 2, 3, 4, 5) { print “$i\n”; }
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5. Loop Control
Ways to control the program flow of Loop block (i.e. Loop Control)
typically used with if or unless
last
terminates the loop
 Example script
next
skips to the next loop iteration
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