Default parameter values in PHP - Mini Project: Build & Apply

Default parameter values

📖 Scenario: Imagine you are creating a simple greeting system for a website. Sometimes visitors provide their name, and sometimes they don't. You want to greet them politely either way.

🎯 Goal: Build a PHP function that greets a user by name if given, or uses a default greeting if no name is provided.

📋 What You'll Learn

Create a function named greet with one parameter $name that has a default value.

Set the default value of $name to 'Guest'.

Inside the function, return a greeting string like 'Hello, NAME!' where NAME is the value of $name.

Call the function twice: once without any argument, and once with the argument 'Alice'.

Print the results of both function calls.

💡 Why This Matters

🌍 Real World

Default parameter values help make functions flexible and easier to use when some information is optional.

💼 Career

Understanding default parameters is important for writing clean, reusable code in PHP and many other programming languages.

1

Create the greet function with a default parameter

Write a PHP function named greet that has one parameter called $name with a default value of 'Guest'. Inside the function, return the string 'Hello, ' . $name . '!'.

PHP

<?php

// Define the greet function with default parameter
// Your code here

Hint

Use = 'Guest' after the parameter $name to set the default value.

2

Call the greet function without arguments

Call the greet function without any arguments and store the result in a variable called $greeting1.

PHP

<?php

function greet($name = 'Guest') {
    return 'Hello, ' . $name . '!';
}

// Call greet without arguments and save to $greeting1
// Your code here

Hint

Call greet() without any parameters to use the default value.

3

Call the greet function with the argument 'Alice'

Call the greet function with the argument 'Alice' and store the result in a variable called $greeting2.

PHP

<?php

function greet($name = 'Guest') {
    return 'Hello, ' . $name . '!';
}

$greeting1 = greet();

// Call greet with 'Alice' and save to $greeting2
// Your code here

Hint

Pass 'Alice' as the argument to greet to override the default.

4

Print both greetings

Print the variables $greeting1 and $greeting2 each on a new line using echo.

PHP

<?php

function greet($name = 'Guest') {
    return 'Hello, ' . $name . '!';
}

$greeting1 = greet();
$greeting2 = greet('Alice');

// Print $greeting1 and $greeting2 each on a new line
// Your code here

Hint

Use echo to print each greeting followed by a newline character "\n".

Practice

1. What is the purpose of default parameter values in PHP functions?

easy

A. To force the user to always pass an argument

B. To make the function run faster

C. To provide a value if no argument is passed when calling the function

D. To declare a variable inside the function

Solution

1. Step 1: Understand default parameters

   Default parameters give a preset value to a function argument if no value is provided during the call.

2. Step 2: Identify the purpose

   This helps avoid errors and makes the function flexible by not requiring all arguments every time.

3. Final Answer:

   To provide a value if no argument is passed when calling the function -> Option C

4. Quick Check:

   Default parameter = fallback value [OK]

Hint: Default values fill in missing arguments automatically [OK]

Common Mistakes:

• Thinking default values speed up the function
• Believing default values force argument passing
• Confusing default parameters with variable declarations

2. Which of the following is the correct syntax to define a function with a default parameter value in PHP?

easy

A. function greet($name = "Guest") { echo "Hello, $name!"; }

B. function greet($name) = "Guest" { echo "Hello, $name!"; }

C. function greet($name: "Guest") { echo "Hello, $name!"; }

D. function greet($name) { $name = "Guest"; echo "Hello, $name!"; }

Solution

1. Step 1: Review PHP default parameter syntax

   In PHP, default values are assigned using the equals sign inside the function parameter list.

2. Step 2: Check each option

   function greet($name = "Guest") { echo "Hello, $name!"; } uses correct syntax: $name = "Guest" inside parentheses. Syntaxes using = after the closing parenthesis or colon (:) are invalid. function greet($name) { $name = "Guest"; echo "Hello, $name!"; } assigns default inside the function body, not as a parameter default.

3. Final Answer:

   function greet($name = "Guest") { echo "Hello, $name!"; } -> Option A

4. Quick Check:

   Default parameter = equals sign in parentheses [OK]

Hint: Use = inside parentheses to set default values [OK]

Common Mistakes:

• Using colon or other symbols instead of =
• Assigning default inside function body instead of parameter list
• Placing default value outside parentheses

3. What will be the output of the following PHP code?

function multiply($a, $b = 2) {
  return $a * $b;
}
echo multiply(5);

medium

A. 7

B. 5

C. Error: Missing argument

D. 10

Solution

1. Step 1: Analyze function call with one argument

   The function multiply expects two parameters, but the second has a default value of 2.

2. Step 2: Calculate the result

   Calling multiply(5) uses $a=5 and default $b=2, so 5 * 2 = 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   5 * default 2 = 10 [OK]

Hint: If argument missing, default value is used [OK]

Common Mistakes:

• Expecting error for missing second argument
• Using wrong default value
• Confusing output with sum instead of product

4. Identify the error in this PHP function definition:

function greet($name = "Guest", $age) {
  echo "Hello $name, age $age";
}

medium

A. Function cannot have default parameters

B. Default parameter must be last or followed only by default parameters

C. Missing semicolon after echo statement

D. Variable names cannot have default values

Solution

1. Step 1: Check parameter order rules

   In PHP, parameters with default values must come after parameters without defaults.

2. Step 2: Identify the error

   Here, $name has a default but $age does not, and $age comes after $name, which is invalid syntax.

3. Final Answer:

   Default parameter must be last or followed only by default parameters -> Option B

4. Quick Check:

   Default parameters must be at the end [OK]

Hint: Place all default parameters after non-default ones [OK]

Common Mistakes:

• Putting default parameters before required ones
• Ignoring PHP syntax rules for parameter order
• Thinking semicolon or variable name causes error

5. Consider this PHP function:

function createUser($name, $role = "user", $active = true) {
  return "$name is a $role and active status is " . ($active ? "yes" : "no");
}

// Call the function
$result = createUser("Alice", active: false);
echo $result;

What will be the output and why?

hard

A. Alice is a user and active status is no

B. Alice is a user and active status is yes

C. Syntax error due to incorrect argument order

D. Error: Named arguments not supported

Solution

1. Step 1: Understand named arguments and defaults

   PHP 8+ supports named arguments, so calling createUser("Alice", active: false) sets $active to false and uses default $role = "user".

2. Step 2: Evaluate function output

   $name = "Alice", $role = "user", $active = false, so output is "Alice is a user and active status is no".

3. Final Answer:

   Alice is a user and active status is no -> Option A

4. Quick Check:

   Named argument sets active=false, role defaults [OK]

Hint: Named arguments can skip defaults, set specific params [OK]

Common Mistakes:

• Assuming named arguments are unsupported in PHP
• Expecting syntax error due to argument order
• Confusing default parameter usage with named arguments