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Control Flow in PHP

In any real application, your code needs to make decisions — showing different outputs based on conditions like user input, login status, or data values. This is where control flow comes in.

In this lesson, you’ll learn how to control the execution of your PHP code using if, else, switch, and the modern match statement. By the end, you’ll be able to write decision-based logic for real-world applications.


What is Control Flow in PHP?

Control flow determines how your program executes based on conditions. Instead of running every line of code, PHP evaluates conditions and decides which block should run.


The if Statement

The if statement runs a block of code only if a condition is true.


Syntax

if (condition) {
    // code to execute
}

Example

$age = 20;

if ($age > 18) {
    echo "You are eligible";
}

Output:

You are eligible

Use case:

Used when you want to execute code only if a specific condition is met.


The if...else Statement

Use else when you want to handle the opposite condition.

$age = 16;

if ($age >= 18) {
    echo "Adult";
} else {
    echo "Minor";
}

Output:

Minor

Use case:

Handling two possible outcomes, such as pass/fail or logged in/not logged in.


The if...elseif...else Statement

Use this when you have multiple conditions.

$marks = 75;

if ($marks >= 90) {
    echo "Grade A";
} elseif ($marks >= 70) {
    echo "Grade B";
} else {
    echo "Grade C";
}

Output:

Grade B

Use case:

Used in grading systems, pricing tiers, or multi-level decisions.


The switch Statement

The switch statement is used when you want to compare a single variable against multiple values.

Example

$day = "Monday";

switch ($day) {
    case "Monday":
        echo "Start of week";
        break;
    case "Friday":
        echo "Weekend coming";
        break;
    default:
        echo "Regular day";
}

Output:

Start of week

Use case:

Cleaner than multiple elseif conditions when checking one variable against many values.


The match Expression (Modern PHP)

The match expression (introduced in PHP 8) is a more concise and strict alternative to switch.

Example

$day = "Monday";

$result = match ($day) {
    "Monday" => "Start of week",
    "Friday" => "Weekend coming",
    default => "Regular day"
};

echo $result;

Output:

Start of week

Why match is Better than switch

  • Uses strict comparison (===)
  • No need for break
  • Returns a value directly
  • Cleaner and less error-prone

Key Difference: switch vs match

Feature         | switch       | match
--------------- | ------------ | --------------
Comparison type | Loose (==)   | Strict (===)
Break required  | Yes          | No
Returns value   | No           | Yes
Syntax          | Verbose      | Clean


Common Mistakes Beginners Make

1. Missing Curly Braces

if ($age > 18)
    echo "Adult";

Why it’s risky:

Only the next line is controlled, which can lead to bugs in larger blocks.

2. Forgetting break in switch

case "Monday":
    echo "Start";

Why it fails:

Execution continues to next case (fall-through bug).

3. Using switch for Complex Conditions

switch ($age > 18) {

Why it’s wrong:

switch is meant for fixed values, not expressions.

4. Expecting Loose Comparison in match

match ("10") {
    10 => "Number"
};

Why it fails:

match uses strict comparison, so this will not match.


Real-World Example

$isLoggedIn = true;
$userRole = "admin";

if ($isLoggedIn && $userRole === "admin") {
    echo "Welcome Admin";
} else {
    echo "Access Denied";
}

Output:

Welcome Admin

What this shows:

  • Logical operators (&&)
  • Comparison (===)
  • Conditional execution


Practice Exercise

Task 1

Check if a number is greater than 50.

Expected Output:

Greater

Task 2

Use if...else to check if a user is logged in.

Expected Output:

Logged In

Task 3

Use switch or match to print day message.

Expected Output:

Start of week


Summary

In this lesson, you learned how control flow works in PHP using if, else, switch, and match. These structures allow your program to make decisions and execute different code based on conditions.

Mastering control flow is essential for building dynamic applications like login systems, dashboards, and user-driven features.

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