Conditional statements are used when we want to perform an action based on a condition. For instance, I can check if it's raining to decide whether to stay home or go out.

Conditional statements have a body structure (wrapped in between curly braces {} ). PHP keywords for condional statements are if, else, else if.

if/else

Decisions in PHP take the following form:

<?php #if-statements.php
   if (condition) { 
      //Code to be executed if condition is true 
   } 
   else 
   { 
      //Alternative code 
   }
?>

The else part of the above is optional. A condition is an expression that can be evaluated to true or false. PHP treats 0 and the empty string as false, and everything else as true. Here is some example code:

<?php #if-statements.php
   $name = "Bill";
   if($name == "Bill")
   { 
      echo "Hi Bill!"; 
   } 
   else 
   { 
      echo "Hello person-who-is-not-Bill"; 
   }
?>

IF statements can be chained together using ELSEIF :

<?php #if-statements.php
   $width = 100;
   $height = 20;

   if($width > $height) 
   { 
      echo "The object is wider than it is high"; 
   } 
   elseif ($width == $height) 
   { 
      echo "The object has similar width and height"; 
   } 
   else 
   { 
      echo "The object is higher than it is wide"; 
   }
?>

An Example:

<?php #if-statements.php
   //declare a variable and assign it a value
   $day = "wed";

   if($day == "wed")
   {
      echo "Today is wednesday";
   }
   else
   {
      echo "Today is not wednesday... Is it thursday?";
   }
?>

Click here to read about switch statements.