Using logical operators in PHP with easy example

Hello friends, this is my third tutorial of PHP and Today I am sharing the concept of using logical operators in PHP. Conditional operators are one of the simple and widely used feature of a programming language. So without wasting any time lets start.
Using if-else structure in PHP :

 <?php 
$a=10;
$b=20;
if($a>$b) {
 echo " A is Greater";
}
elseif($a<$b) {
 echo " A is lesser";
}
else {
 echo "A and B are equal";
}
?>

Using if-else structure with multiple conditions in PHP :

 <?php 
$c=30;
$d=40;
//if(($a<$c)AND($b<$d))
if(($a<$c)&&($b<$d)) {
 echo "A and B are larger";
}
if(isset($d)) //Checks if a variable is initialized or not
$d=100;
echo $d;
unset($d);
?>

Using switch-case in PHP :

 <?php 
$var1=2;
switch($var1)
{
 case 1 : echo "var1 is 1";
         break;
 case 2 : echo "var1 is 2";
         break;
 case 3 : echo "var1 is 3";
         break;
 default : echo "var1 is unknown";
}
?>