Ch-5 Identifier in PHP
Like C and
other programming languages we need to
declare and define identifier in PHP also, to create memory name and store data
in that particular memory name space.
But in PHP
we have no need to specify data type of identifier.
Identifier
Declaration Rule:
<?php
$a=10;
echo $a
?>
Output-10
1. Start with any letter,
number,underscore
(remember, can not use any other special character,
only underscore allowed ) eg. $1a;$_a;
2. Identifier is a case sensitive.eg.
$a=10, $A=20; both are different
3. Identifier name cannot be identical;
means it cannot be match by predefine keyword.
There are 2 type of Identifier:
1. Variable
2. Constant
Variable:
a. Variable name followed by $ sign. For
eg.
$a; here a is an variable declaration.
b. Variable can be change as so many
time for eg.
i.
$a=10;
, php automatic create integer type memory location and store 10 .
ii.
$a=15.8;
, php automatic create floating type memory location and store 15.8 in place of
10.
<?php
$a=10;
echo $a;
$a=15.8;
echo nl2br("\n$a");
?>
Output
10
15.8
First time $a store 10, then it store
15.8.
Here nl2br is a line break or new
line function
Remember,
like C , \n can not directly use with echo
Constant:
a. Constant value cannot be change
during program life.
b. Constant name cannot be followed by $
sign.
c. Only starts with any letter or
underscore.
d. For create identifier as a constant
,we need define() function, with 2 argument:
i.
Constant
name and
ii.
Value
of that constant
For ex. Define(‘a’,10);
a is a constant name and 10 is a
constant value of a.
Difference between variable and reference variable
From above we already discussed about
variable that, variable name stats with a 4 sign which hold such a value which
can be edit or change.
Like a variable, there is a another type
of variable available in php , known as Reference variable.
Reference variable starts with double
dollar ($$) ,this variable is used for reference of predefine variable value.
With the help of variable reference
we can change another related variable value.
For ex.
<html>
<head><title>strtest</title></head>
<body bgcolor="red" text="green">
<?php
$x="abc";
$$x=20;
echo '$x is'.$x,'
<br>$abc is',$abc,' <br>$$x is'.$$x;
echo "<br><br><br>";
echo "if I will change $abc is 80 by ($abc=80;) then
further value will be";
$abc=80;
echo "<br> <br> <br> <br>
";
echo ' now the value of $abc is'. $abc ,' <br> new
value of $$x is'.
$$x ,'<br> $x is
'. $x ;
?>
$x isabc
$abc is20
$$x is20
if I will change 20 is 80 by (20=80;) then further value will be
now the value of $abc is80
new value of $$x is80
$x is abc
$abc is20
$$x is20
if I will change 20 is 80 by (20=80;) then further value will be
now the value of $abc is80
new value of $$x is80
$x is abc
change in $abc value also changes $$x
value
There are also many way to print
string in php , you can also code such above program like :
<html>
<head><title>strtest</title></head>
<body bgcolor="red" text="green">
<?php
$x="abc";
$$x=20;
?>
<p>value of $x is <?php echo $x ?> <br>
value of $$x is <?php echo $$x ?>
and<br> $abc is <?php echo $abc
?><br></p>
<?php
$abc=80;
echo "<br>";
echo $$x;
?>
<p> now the value of $abc is <?php echo $abc ?>
<br> new value of $$x is
<?php echo $$x
?><br> $x is <?php echo $x ?></p>
</body>
</html>
Output:
value of $x is abc
value of $$x is 20and
$abc is 20
value of $$x is 20and
$abc is 20
80
now the value of $abc is 80
new value of $$x is 80
$x is abc
new value of $$x is 80
$x is abc
OR
In above 2 program you can use html
character set value in place of $ sign. For eg.
<?php
$x=90;
echo "$x value is $x";
?>
This program print : $x value is 90
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