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Default parameter values

PHP course · Beginner · Lesson 78/116

Learn to assign a default value to a parameter so it can be skipped at the call.

Default value

You can assign a default value to a parameter. This is the value used when the caller skips that argument. The assignment uses = inside the parentheses.

Example: function greet($name = "Guest") { echo $name; }. The call greet("Alex") prints "Alex"; the call greet() passes no argument, so the default "Guest" is used and "Guest" is printed.

Optional parameter

Parameters with a default are optional: the caller may skip them. This is handy for values that are the same in most calls.

For example in function logMessage($msg, $level = "INFO") { echo "[" . $level . "] " . $msg; } the $level is optional. The call logMessage("Started") skips $level and uses "INFO"; the call logMessage("Error", "ERROR") passes "ERROR" to $level. Optional parameters must always come after required ones.

Exercise Print a log message

Define a function logMessage with parameters $msg and $level = "INFO". In the body write echo "[" . $level . "] " . $msg . "\n";. Then call logMessage("System started") first and logMessage("Connection lost", "ERROR") second.

Show example solution 
Define function logMessage($msg, $level = "INFO") { ... }, put echo "[" . $level . "] " . $msg . "\n"; in the body. The first call takes one argument logMessage("System started");, the second takes two logMessage("Connection lost", "ERROR");.
Example solution:
<?php
// Define logMessage and call it twice
function logMessage($msg, $level = "INFO") {
    echo "[" . $level . "] " . $msg . "\n";
}
logMessage("System started");
logMessage("Connection lost", "ERROR");

Test yourself

  1. Complete the default value

    function greet($name____) { echo $name; }
    Show answer 
    function greet($name = "Guest") { echo $name; }

  2. What is the output of the following code?

    function greet($name = "Guest") {
    echo $name;
}
greet();
    • $name
    • (empty output)
    • Guest
    • PHP error
    Show answer

    Guest — Correct. With no argument passed, $name takes its default 'Guest'.

  3. Match default value concepts

    Default value
    Used when no argument is passed
    $name = "Guest"
    Default value syntax
    Optional
    A parameter with a default

All lessons in Beginner

1 PHP basics

  1. What is PHP?
  2. PHP tags
  3. Output with echo
  4. Comments
  5. phpinfo() and PHP version
  6. Summary - PHP basics

2 Variables

  1. Declaring variables
  2. Variable naming rules
  3. Reassigning variables
  4. Combining variables
  5. Checking variables with isset() and unset()
  6. Summary - Variables

3 Data types

  1. string and int
  2. float and bool
  3. null and empty value
  4. Type checking with gettype()
  5. Detailed output with var_dump()
  6. Summary - Data types

4 Project: Calculator

  1. Project: Calculator
  2. Number input and operator selection
  3. Computing the operation
  4. Handling error cases
  5. Project final - Calculator

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Concatenation and increment
  6. Summary - Operators

6 String basics

  1. Creating strings
  2. Length with strlen()
  3. String concatenation
  4. Variable interpolation in double quotes
  5. Escape sequences
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and elseif
  3. The switch statement
  4. The ternary operator
  5. Comparison pitfalls
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. The foreach loop
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Project: Shopping cart
  2. Adding products to the cart
  3. Displaying the cart
  4. Computing the total
  5. Project final - Shopping cart

10 Array basics

  1. Creating arrays
  2. Accessing array elements
  3. Element count with count()
  4. Array output with print_r()
  5. Iterating an array
  6. Summary - Array basics

11 Array methods

  1. array_push() and array_pop()
  2. array_shift() and array_unshift()
  3. Merging with array_merge()
  4. Slicing with array_slice()
  5. in_array() and array_search()
  6. Summary - Array methods

12 Associative arrays

  1. Key-value pairs
  2. Accessing keys
  3. array_keys() and array_values()
  4. Key check with isset()
  5. Iterating associative arrays
  6. Summary - Associative arrays

13 Functions

  1. Defining functions
  2. Calling functions
  3. Returning values
  4. Function scope
  5. Returning arrays from functions
  6. Summary - Functions

14 Parameters

  1. Functions with parameters
  2. Default parameter values
  3. Multiple parameters
  4. Typed parameters
  5. Return type declaration
  6. Summary - Parameters

15 Project: To-do list

  1. Project: To-do list
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Project final - To-do list

16 Advanced string methods

  1. Replacing with str_replace()
  2. Slicing with substr()
  3. Searching with strpos()
  4. Splitting with explode()
  5. Joining with implode()
  6. Summary - Advanced string methods

17 Superglobals

  1. What is a superglobal?
  2. Receiving data with $_GET
  3. Receiving data with $_POST
  4. $_SERVER and server info
  5. Everything with $_REQUEST
  6. Summary - Superglobals

18 Forms

  1. Creating HTML forms
  2. Processing form data
  3. Security with htmlspecialchars()
  4. Form validation basics
  5. Showing error messages
  6. Summary - Forms

19 File inclusion

  1. Including files with include
  2. Including files with require
  3. include_once and require_once
  4. __DIR__ and path management
  5. Layout and partial logic
  6. Summary - File inclusion

20 Beginner final

  1. Challenge - Calculator
  2. Challenge - Secure feedback form
  3. Challenge - Array operations
  4. Challenge - Functions and loops
  5. Challenge - Mini CMS