In PHP, nested if, else, and elseif statements are used to handle complex decision-making scenarios by placing one or more if-else or elseif statements inside another if or else block. This allows you to evaluate multiple conditions in a hierarchical manner.

Basic Structure

Nested if Statements

An if statement inside another if statement is called a nested if statement.

Syntax:

if (condition1) {
    // Code to be executed if condition1 is true
    if (condition2) {
        // Code to be executed if condition2 is true
    } else {
        // Code to be executed if condition2 is false
    }
} else {
    // Code to be executed if condition1 is false
}

Example:

<?php
$age = 25;
$hasID = true;

if ($age >= 18) {
    if ($hasID) {
        echo "You can enter the club.";
    } else {
        echo "You need an ID to enter.";
    }
} else {
    echo "You are too young to enter.";
}
?>

Explanation:

• The outer if checks if $age is 18 or older.
• If true, the inner if checks if $hasID is true.
• Depending on whether $hasID is true or false, the appropriate message is displayed.
• If the outer if condition is false (i.e., the person is younger than 18), the else block of the outer if is executed.

Nested if-else Statements

You can also nest if-else statements where an else block contains another if-else statement.

Syntax:

if (condition1) {
    // Code to be executed if condition1 is true
} else {
    if (condition2) {
        // Code to be executed if condition2 is true
    } else {
        // Code to be executed if condition2 is false
    }
}

Example:

<?php
$score = 75;

if ($score >= 80) {
    echo "Grade: A";
} else {
    if ($score >= 60) {
        echo "Grade: B";
    } else {
        echo "Grade: C";
    }
}
?>

Explanation:

• The outer if checks if $score is 80 or more, assigning grade A if true.
• If the outer condition is false, the nested if-else statement evaluates whether $score is 60 or more to assign grade B, or otherwise assigns grade C.

Nested if-elseif-else Statements

if-elseif-else statements can also be nested inside each other to handle more complex logic.

Syntax:

if (condition1) {
    // Code to be executed if condition1 is true
} elseif (condition2) {
    // Code to be executed if condition2 is true
    if (condition3) {
        // Code to be executed if condition3 is true
    } else {
        // Code to be executed if condition3 is false
    }
} else {
    // Code to be executed if both condition1 and condition2 are false
}

Example:

<?php
$score = 85;

if ($score >= 90) {
    echo "Grade: A";
} elseif ($score >= 80) {
    if ($score >= 85) {
        echo "Grade: B+";
    } else {
        echo "Grade: B";
    }
} else {
    echo "Grade: C or below";
}
?>

Explanation:

• The outer if checks if $score is 90 or more, assigning grade A if true.
• The elseif block checks if $score is 80 or more and contains another if to further categorize scores into B+ or B based on whether the score is 85 or more.
• If neither condition is met, it assigns "Grade: C or below."