if else statement in PHP with examples

This article is created to cover the three conditional statements used in PHP, which are:

• if
• if...else
• if...elseif...else

if statement in PHP

The PHP "if" statement is used when we need to execute some blocks of statements (codes) when a specified condition is true. For example:

<?php
   $num = 10;
   if($num==10)
   {
      echo "The value of \$num is 10";
      echo "<BR>";
   }
?>

The output produced by the above PHP example is shown in the snapshot given below:

In the preceding example, the condition "$num==10" or "10==10" (as the value of $num has been initialized by 10) evaluates to true.Therefore, the program flow goes inside the if body and executes the two written statements. The first statement prints the value of $num, whereas the second statement inserts a line break using the BR tag.

The above program can also be written in this way:

<?php
   $num = 10;
   if($num==10)
      echo "The value of \$num is 10<BR>";
?>

Since there is a single statement available as the body of if, there is no need to put the statement inside curly braces or {}. A single statement does not require that you write inside a curly brace. However, you can use curly braces for single statements too.

The syntax of the if statement in PHP is:

if(condition)
{
   // block of code to execute if condition is true
}

if...else statement in PHP

The PHP if...else block is used when we need to execute some block of code when the specified condition evaluates to be true and some other block of code when the specified condition evaluates to be false. For example:

<?php
   $num = 20;
   if($num==10)
      echo "The value of \$num is 10";
   else
      echo "The value of \$num is not 10";
?>

The output of this PHP example should be:

The value of $num is not 10

Since the condition $num==10 or 20==10 evaluates to be false, the program flow goes inside the else body, and the statement available inside the else body gets executed.

That is, the program executes the block of code available in the body of if when the condition evaluates to be true. Otherwise, the program executes the block of code available in the body of the counterpart of if, that is, else, when the condition evaluates to be false.

The syntax of the if...else statement in PHP is:

if(condition)
{
   // block of code to execute if condition is true
}
else
{
   // block of code to execute if condition is false
}

if...elseif...else statement in PHP

The PHP if...elseif...else statement is used when we need to execute a particular block of code based on multiple conditions. For example:

<?php
   $num = 0;
   if($num<0)
      echo "The value of \$num is a negative number.";
   elseif($num==0)
      echo "The value of \$num is 0.";
   else
      echo "The value of \$num is a positive number.";
?>

The output of this PHP example should be:

The value of $num is 0.

The syntax of the if...elseif...else statement in PHP is:

if(condition_1)
{
   // block of code to execute, if condition_1 is true
}
elseif(condition_2)
{
   // block of code to execute, if condition_2 is true
}
elseif(condition_3)
{
   // block of code to execute, if condition_3 is true
}
elseif(condition_4)
{
   // block of code to execute, if condition_4 is true
}
.
.
.
elseif(condition_N)
{
   // block of code to execute, if condition_N is true
}
else
{
   // block of code to execute, if all conditions are false
}

If multiple conditions evaluate to be true, for example, let's suppose that condition_2 and condition_3, both evaluate to be true. In that case, the first condition that evaluates to true is executed, and the rest is skipped. For example:

<?php
   $x = -10;
   if($x > -10)
      echo "The value of \$x is greater than -10";
   elseif($x == -10)
      echo "The value of \$x is -10";
   elseif($x < 0)
      echo "The value of \$x is less than 0";
   elseif($x == 0)
      echo "The value of \$x is 0";
   elseif($x > 0)
      echo "The value of \$x is greater than 0";
   else
      echo "The value of \$x is unknown";
?>

Since the conditions $x == -10 and $x < 0 are both true, but first the condition $x == -10 has been evaluated, the block of code available inside that block will be executed, and the rest of the execution of the same if...elseif...else structure gets skipped. Therefore, the output should be:

The value of $x is -10

Advantages and disadvantages of the if, if...else, and if...elseif...else statements in PHP

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