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Flow control

First you have the operators:

• Mathematical operators
• Compare operators
• Logical operators

Then you have the statements:

• If statement
• While statement
• For statement
• Foreach statement

 

Mathematical operators

Operator	calculation	example
+	add	3+3
-	minus	3-1
*	multiply	3*3
/	divide	3/3

Compare operators

Operator		calculation	example
Number	String
==	eq	equals	$string eq "tom"
!=	ne	is not equal	$string ne "tom"
>	gt	is larger then	$number > 20
<	lt	is smaller then	$number < 20
>=	ge	is larger then or equal	$number >= 20
<=	le	is smaller then or equal	$number <= 20

Logical operators

Operator	Description	Example
||	Logical OR	$number1 > 20 || $number2 < 20
&&	Logical AND	$number1 > 20 && $number2 < 20
!	Logical NOT	! $number1 > 20

IF statement

Well you know, if works as follows: if the statement is true, then this happens, when it is false, that happens.

print "how old are you?";

chomp ($age =<STDIN>);

if '$age < 18)
{
  print "Sorry, you're not old enough!";
}
else
{
  print "You're old enough to enter";
}

The else part is optional.

print "How old are you?";

chomp ($age =<STDIN>);

if '$age < 18)
{
  print "Sorry, you're not old enough!";
}

In a if-statement you can make multiple tests. You have to add elsif.

print "How old are you?";

chomp ($age =<STDIN>);

if '$age < 18)
{
  print "Sorry, you're not old enough!";
}
elsif (&age == 18)
{
  print "Cool, you're just old enough!";
}
else
{
  print "You're old enough!";
}

Besides the if statement, you can also use the terminator ?:.

($a < 10) ? ($b = $a) : ($a = $b);

It can be usefull to only use the else part. You can do this with the unless statement. Perl will execute the unless-part when the result is FALSE.

print "How old are you ?";

comp ($age= <STDIN>);

unless ($age < 18)
{
  print "You're old enough to enter!";
}

While statement

A while statement repeats the same code while a statement is true. You have to make sure that something in the code change the statement at 1 time.

print "How old are you ?";

comp ($age= <STDIN>);

while ($age > 0)
{
  print "at one time, you were $age years old!\n";
  $age--;
}

for statement

A for statement exist of 3 parts= the initialization, the test and a increment/decrement.

@names=("Tom","Bert","Frank","Eli","Brigitte");

for ($i=0; $i <= $#names; $i++)
{
  print "$names[$i]";
}

Foreach statement

A foreach statement shall assign a value from a list to a variable and then do the statements until you reach the end of the list.

@names=("Tom","Bert","Frank","Eli","Brigitte");

foreach $person (@names)
{
  print "$person \n";
}

You don't have to write $person. The following code will do exactly the same.

@names=("Tom","Bert","Frank","Eli","Brigitte");

foreach (@names)
{
  print "$_ \n";
}

 

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