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If Statement:

The If statement is used to execute a block of code when the condition is evaluated to be true. When the condition is evaluated to be false, the program will skip the if-code block.

Syntax

if(condition) {
  statements;
}

Flow Diagram:

PHP If Loop

In the below example, the if code block is created which executes only when the variable called i is divisible by 3.

<?php
$i = 15;
if ( $i % 3 == 0) {
  echo $i." is divisible by 3.\n"; 
}
?>

The output of the above code will be:

15 is divisible by 3.

If-else Statement:

The else statement is always used with If statement. It is used to execute block of codes whenever If condition gives false result.

Syntax

if(condition) {
  statements;
}
else {
  statements;
}

Flow Diagram:

PHP If-else Loop

In the below example, else statement is used to print a message if the variable i is not divisible by 3.

<?php
$i = 16;
if ($i % 3 == 0){
  echo $i." is divisible by 3.\n"; 
}
else {
  echo $i." is not divisible by 3.\n"; 
}
?>

The output of the above code will be:

16 is not divisible by 3.

elseif Statement:

For adding more conditions, else if statement in used. The program first checks if condition. When found false, then it checks else if conditions. If found false, then else code block is executed.

Syntax

if(condition) {
  statements;
}
elseif(condition) {
  statements;
}
...
...
...
else {
  statements;
}
}

Flow Diagram:

PHP If-elseif-else Loop

In the below example, else statement is used to print a message when all if and else if conditions result false.

<?php
$i = 16;
if ($i > 25){
  echo $i." is greater than 25.\n"; 
}
elseif($i <=25 && $i >=10){
  echo $i." lies between 10 and 25.\n"; 
}
else{
  echo $i." is less than 10.\n"; 
}
?>

The output of the above code will be:

16 lies between 10 and 25.