Block Structures and Loops
This document was written by CS 290W TA David Corcoran and was last
modified
Like other programming languages, Perl supports mostly the same style of
Block Statements and Loops.
if, elsif, else
<![CDATA[
if ( $iAge < 13 )
{
print "This student is not yet a teenager. \n";
}
elsif ( ( $iAge >= 13 )&&( $iAge <= 17 ) )
{
print "This student is a teenager. \n";
}
else
{
print "This student is an adult. \n";
}
]]>
Everything looks the same right? Look again. Notice the elsif. Is that
a misspelling? No it is not. An else if statement in Perl is actually
elsif.
Unless Statement
<![CDATA[
unless ( $iAge < 21 )
{
print "Welcome to Harry's. \n";
}
]]>
The above statement only is executed if $iAge >= 21. Basically it is
performing the given operation if the statement in the unless block is
False.
While Statement
<![CDATA[
$iAge = 13;
while ( $iAge < 21 )
{
print "You are too young to enter. \n";
$iAge += 1;
}
]]>
The above statement will continue to execute until $iAge is greater than
or equal to 21.
Until Statement
<![CDATA[
$iAge = 13;
until ( $iAge >= 21 )
{
print "You are too young to enter. \n";
$iAge += 1;
}
]]>
The above statement will also be executed until $iAge is greater than or
equal to 21. This works similar to the Unless Statement in that it
executes while the enclosed statement is False.
For Statement
<![CDATA[
for ( $iCount = 0; $iCount < 21; $iCount++ )
{
print "Counting from 0 to 20 $iCount. \n";
}
]]>
The above statement sets $iCount to zero and executes until $iCount is
less than 21. It increments $iCount during this process. This should
count from 0 to 20. Notice how you can embed scalars right into a
print statement regardless of their type.