The if else & elseif Statements in PHP

<?php
$user_age = 20;

if ($user_age >= 18) 
{
    echo "You are an adult.";
}
?>

The code checks if the $user_age variable is 18 or more. If true, it prints the message. The condition uses the >= comparison operator. Only one statement executes when the condition is met.

<?php
$current_temperature = 15;

if ($current_temperature > 20) 
{
    echo "It's hot outside.";
} 
else 
{
    echo "It's not too hot.";
}
?>

The code checks if the current temperature exceeds 15 degrees. If not, the else block executes. This provides a default action when the condition fails. Only one of the two blocks will ever execute.

<?php
declare(strict_types=1);

$grade = 85;

if ($grade >= 90)
{
    echo "Grade: A";
} 
elseif ($grade >= 80) 
{
    echo "Grade: B";
} 
elseif ($grade >= 70) 
{
    echo "Grade: C";
} 
else 
{
    echo "Grade: F";
}
?>

The code checks the grade against multiple thresholds. It stops at the first true condition. The else provides a default for grades below 70. This pattern is common for grading systems.

<?php
declare(strict_types=1);

$user_age = 25;
$user_has_license = true;

if ($user_age >= 18)
{
    if ($user_has_license) 
	{
        echo "You can drive.";
    } 
	else 
	{
        echo "You need a license.";
    }
} 
else 
{
    echo "You're too young to drive.";
}
?>

The outer if checks user age, while the inner one checks user license status. This creates a hierarchical decision structure. Each condition must be true for the innermost block to execute.

<?php
declare(strict_types=1);

$isMember = true;
$orderTotal = 120;

if ($isMember && $orderTotal > 100) 
{
    echo "You qualify for free shipping!";
} 
elseif ($isMember || $orderTotal > 150) 
{
    echo "You get 10% discount.";
} 
else 
{
    echo "No special offers available.";
}
?>

The code checks combinations of conditions using && (AND) and || (OR). The first condition requires both to be true. The second needs either one true. Logical operators allow complex condition combinations.

<?php
declare(strict_types=1);

$isLoggedIn = true;
$message = $isLoggedIn ? "Welcome back!" : "Please log in.";

echo $message;
?>

The ternary operator evaluates the condition before the ?. If true, it returns the first expression, otherwise the second. This is useful for simple decisions. It's more compact than full if-else blocks.

<?php
declare(strict_types=1);

$user = array(
    'name' => 'Kenneth Roggers',
    'age' => 25,
    'active' => true
);

if (!empty($user['name']) && $user['active']) 
{
    echo "Welcome, {$user['name']}!";
} 
elseif (empty($user['name'])) 
{
    echo "Please set your name.";
} 
else 
{
    echo "Account not active.";
}
?>

The code checks multiple array elements in conditions. It first verifies the name exists and account is active. The empty function checks for non-empty values. array conditions work like variable conditions.