4.1 Introduction to PHP

Prerequisites
- HTML5, especially <form>

Learning objectives
- Basic programming with PHP in the web application environment
- Understanding and use of interaction with the client-side
  - Super global arrays
  - echo()

Difference between client-side JavaScript and server-side PHP

	Runtime environment	Main usage	Number of files	Visibility of source code on web browser
client-side JavaScript	Web browser	Event-driven programming, Access to HTML elements	Usually one	Yes
server-side PHP	Web server + operating system	Access to database, Send data and/or client-side web content back to the client	Usually multiple	No

PHP basic
- PHP 8.3.6 on cs.tru.ca
- Read 'What is a PHP file?', 'What Can PHP Do?', 'Why PHP?' in PHP Introduction.
  - What is the default file extension for PHP files?
  - What receives the URL sent from the client?
  - What executes the PHP file specified by the URL sent from the client?
  - What does PHP code send to the client browser?
  - Anything but PHP code will be sent back to the client? Here is a test PHP program (test.php).
  - What happens when PHP code completes its tasks?
  - In a web browser, can you read the source code of a PHP program? This is a very important concept.
- Read all in PHP Syntax.
  - What kind of tags are used for PHP code?
  - What are the three comment types?
  - Is PHP case sensitive? It is interesting.
  - How to declare PHP variables?
  - How to concatenate strings?
  - How to output strings to the client?
  - Trial 1: Let's try the next example.
    <??? echo 'Very interesting!<br>'; ???> <h2>What a wonderful world!</h2> <script> console.???('A dead thing can go with the stream, but only a living thing can go atainst it.'); </script>
- Read all in PHP Variables and PHP Variables Scope.
  - How to declare PHP variables?
  - Is PHP loosely typed language or strongly typed language?
  - How is a variable within a string defined using single quotes interpreted? How is a variable within a string defined using double quotes interpreted?
  - What symbol is used for string concatenation?
  - What are the three different types of variable scope?
  - How to declare a function?
  - How are global variables different from local variables?
  - How to access global variables in a function?
  - How to declare static variables?
  - How are static variables different from other non-static local variables?
  - Trial 2: Let's try the next example.
    <?php $x = 10; $y = 20; function try2_ft1($z) { $x = $x + $z; // ??? echo $x . '<br>'; } ??? try2_ft2($y) { static $z = 30; // ??? $z += $y; ??? $z . '<br>'; } try2_ft1(5); try2_ft2(15); try2_ft2(15); echo $x . '<br>'; echo $z . '<br>'; // ??? ?>
- Read all in PHP echo and print Statements.
  - Which statement is faster?
  - Which statement can output multiple strings?
  - How is "..." different from '...'?
    - Single quoted strings will display things almost completely "as is." Variables and most escape sequences will not be interpreted. The exception is that to display a literal single quote, you can escape it with a back slash \', and to display a back slash, you can escape it with another backslash \\ (So yes, even single quoted strings are parsed).
    - Double quote strings will display a host of escaped characters (including some regexes), and variables in a double quote string will be evaluated. An important point here is that you can use curly braces to isolate the name of a variable you want to evaluate. For example let's say you have the variable $type and you want to echo "The $types are" . That will look for the variable $types. To get around this use echo "The {$type}s are". You can put the left brace before or after the dollar sign. Take a look at string parsing to see how to use array variables and such.
  - Trial 2.5: Let's try the next example.
    <?php $car = 'VW Golf'; echo 'My favorite car is $car.<br>'; echo "My favorite car is $cars.<br>"; echo "My favorite car is {$car}s.<br>"; echo ????; // How to include {...} in the string? {{...}} echo "My favorite car is " . $car . " <br>"; ?>
- Read all in PHP Data Types.
  - What are the two Boolean values?
  - How to obtain the quotient from an integer division? Note that there is no 'integer division' in PHP.
  - List 7 data types.
  - How to define an array? Always the same type values?
  - How to access an array element?
  - Use of var_dump() with an array.
  - How to define a function?
  - How to define a class?
  - How to create/instantiate an object?
  - How to access properties in an object?
  - We will revisit 'Classes and Objects' again.
  - Is NULL value an empty string?
  - Trial 3: Let's try to write the code to save some information into an array and print it using 'var_dump()'. You need to include three values, 'John', 23, and true, in the array, where true is a Boolean value, not a string.
    <?php $student = ???(????); // or $student = [ ... ]; echo 'Name = ' ??? $student[???] . '<br>'; ???($student); ?>
- Read all in PHP String.
  - How to get the length of a string? Are strings objects?
  - How to search a specified character or text within a string?
  - What value is returned from strpos() when a specific text is not found? Isn't it interesting?
  - PHP String Functions for full reference
  - How to get a substring of a string?
  - How to compare two strings?
  - Important functions - strlen, strcmp, implode and join, explode, trim, ...
  - Trial 4: Let's try the next example with some string functions, strcmp(), strlen() and trim().
    <?php $str1 = ???; // Any string $str2 = ???; $result = ???(???, ???); // Compare the two strings echo $result . '<br>'; // Comparison result echo ???($str1 ??? $str2) . '<br>'; // Length of the concatenated string $str = ' What a wonderful world! '; echo '***' . $str . '***' . '<br>'; $str = ???($str); // Trim all the white spaces around the string echo '***' . $str . '***' . '<br>'; ?>
  - Trial 5: Let's try to use implode(separator, array) and explode(separator, string) functions.
    <?php $students = ???(????); // A array of student names; You may use [...] instead. echo var_dump($students) . '<br>'; $str = ???(', ', $students); // Join the values stored in the above array echo $str . '<br>'; $students2 = ???(???, $str); // Convert the string to an array ???($students2) . '<br>'; ?>
- Read all in PHP Constants.
  - How to define a constant and use it?
  - Are constants global? What if a constant is defined in a function?
- Read all in PHP Operators.
  - What is the output 'echo 6 / 4'?
  - How to concatenate two strings?
  - Identical operator and not identical operator?
  - Logical operators?
  - How to make the union of two arrays?
  - Integer division?
  - Trial 6: Let's try some operations. Integer division, or floating-point number division? Hint, floor().
    <?php echo ??? . '<br>'; // 6/4 echo 6 ??? 4 . "<br>"; // 6 to the power of 4; It may not be supported.; phpinfo() to see the version of PHP echo ????; // integer division? ?>
- Comparison to JavaScript
  - Tags
  - Declaration of variables
  - Access to global variables
  - String concatenation operator, exponentiation operator
  - The way to obtain the string length
  - The static keyword
  - Creation of arrays. Can you use [...]? From PHP 5.4
  - The way to obtain the number of elements in an array
  - Union of two arrays
  - echo
  - Trial 7: Let's try to create an array using [...], not array().
    <?php $students = [????]; // two student names $courses = array(????); // three course numbers echo var_dump($students) . '<br>'; echo var_dump($courses) ???; $unioned = $students ??? $courses; // Union of two arrays, not concatenation echo var_dump($unioned) ???; echo ???($unioned); // The number of elements ?>

PHP control statements
- Read all in PHP if...else...elseif Statements.
  - date()
- Read all in PHP switch Statements.
  - Can you convert an if-else statement to a switch statement?
  - Can you convert a switch statement to an if-else statement?
  - When do you use a break statement?
- Read all in PHP while Loops.
  - How is while loop different from do-while loop?
- Read all in PHP for Loops and PHP foreach Loops.
  - How is foreach-as loop different from for loop?
  - How is foreach-as loop different from for-in loop in JavaScript?
  - Trial 8: Let's try to write the code to save some information into an array an print it using a 'foreach' loop. You need to include 'John', 23, true in the array.
    <?php $student = ???(????); echo 'Name = ' ??? $student[???] . '<br>'; ??? (????) echo ???; ?>
- Read all in PHP Arrays, PHP Indexed Arrays, and PHP Associative Arrays.
  - How to count the data in an array?
  - How to use associative arrays?
  - How is foreach-as loop different from for-in loop in JavaScript?
  - Trial 9: Let's try to write the code to save some information into an associative array and print it using a 'foreach' loop. You need to include Huyndai:Sonata, VW:Golf, Honday:CR-V in the array.
    <?php $cars = ????; echo 'The number of cars is ' . ???($cars) . '<br>'; ??? (????) // for each element ????; // display key and value ?>
  - Trial 9.5: Let's try to write the code that sends the <table> code to the client. The <table> needs to be constructed within a function. The table cells need to include values from an associative array using a 'foreach' loop. You need to include Hyundai:Sonata, VW:Golf, Honda:CR-V in the array.
    <?php ???? { $str = "<table border='1'>"; $str ???= '<tr>'; // tr for keys ??? ($cars ??? $k ??? $value) $str .= '<th>' . ??? . '</th>'; $str .= "</tr>"; ???? // tr for values ??? (????) $str ???? ???? $str .= ???; ???? } $cars = ["Hyundai"=>"Sonata", "VW"=>"Golf", ???]; echo ????; // display the table code with the above function ?>
- Comparison to JavaScript
  - Creation of arrays
  - foreach-as vs for-in

PHP functions
- Read all in PHP Functions.
  - How to create a function?
  - How to use default argument values?
  - How to use default argument values in JavaScript?
```
function defaultftexample(a, b){
    if(typeof a == 'undefined')  // Or typeof(a)
        a = 10;
    if(b == undefined) 
        b = 20;
    ...
}
function anotherexample(a = 10, b) {
    ...
}
```
- Comparison to JavaScript
  - Default argument values
  - Call by reference

PHP arrays and superglobals
- Read all in PHP Arrays.
  - How to create an array?
  - List the three types of array.
  - How to count the number of elements in an array? .length()?
  - Which loop fits indexed (linear) arrays?
  - How to create an associative array?
  - How to access an element in an associative array?
  - Which loop fits associative arrays?
  - How to use foreach-as with associative arrays?
- Read all in PHP Sorting Arrays. You may read JavaScript Sorting Arrays for JavaScript.
  - How to sort an array in ascending/descending order?
  - How to sort an associative array, according to the value/key?
  - Study closely the return value of the sorting functions.
- PHP Array Functions for full reference
  - Can you make a stack?
  - Can you make a queue?
  - Can you search a value in an array?
  - Trial 10: Let's try to make a stack and a queue. You may use in_array(), array_push(), array_pop(), array_shift(), array_unshift().
    <?php $cars = ???; // Empty array ???($cars, 'Elentra'); // Add a car name at the end ???($cars, 'Golf'); // Add a car name at the end ???($cars, 'CR-V'); // Add a car name at the end echo var_dump($cars) . '<br>'; $result = ???('Prius', $cars); // Check if 'Prius' is in the array echo $result . '<br>'; $car = ???($cars); // Take out the last one echo $car . '<br>'; echo var_dump($cars) . '<br>'; $car = ???($cars); // Take out the first one echo $car . '<br>'; echo var_dump($cars) . '<br>'; ?>
- In client-side JavaScript, how to access the runtime environment?
  window and document
- In PHP, how to access the runtime environment?
- Read all in PHP Global Variables - Superglobals.
  - What are superglobal variables? Are they visible in user-defined functions without using the 'global' keyword?
  - What superglobal variable is used to access any global variables?
  - What information is stored in $_SERVER?
  - How $_POST is different from $_GET?
  - "http://stackoverflow.com/questions/1924939/php-request-vs-get-and-post": $_REQUEST, by default, contains the contents of $_GET, $_POST and $_COOKIE. But it's only a default, which depends on variables_order ; and not sure you want to work with cookies. If I had to choose, I would probably not use $_REQUEST, and I would choose $_GET or $_POST
  - For what do you need super global arrays? Data transfer from web server to PHP code
  - Trial 11: Let's try to print all the values in $_GET and $_POST.
    <h1>TRU Question & Answer</h1> <?php /* Just for testing; In the real situation, GET and POST data will be sent from client-side programs. */ $_GET['username'] = 'John'; $_GET['password'] = 'topsecretpassword'; $_GET[???] = ???; // Anything // Or $_GET = ['username'=>'John', ...]; All other $_GET[] values will be destroyed. ?> <h1>Welcome <?php echo ???['username']; ?>!</h1>  <?php ???? // For each element in $_GET[] echo ???? . '<br>'; // display key and value ?>
- Comparison to JavaScript
  - Creation of associative arrays
  - Call by reference
  - Super global arrays

How to send and receive data
- Read all in PHP Form Handling.
  - Which superglobal variables are used to collect form data?
  - When do you use 'get'?
  - When do you use 'post'?
  - Is the value in a hidden-type input element also submitted?
  - Note that the server-side action script sends data, i.e., web contents, back and they will be displayed in the new window, meaning a new web application, not the current window.
  - You may review 3.12.
- How to send multipe values with one name?
  - The names of input-like elements should be attached with [], like an array.
  - Here is an example.
```
<form action='//cs.tru.ca/~mlee/comp3540/Software/test_display_inputs.php' method='get'>
    <select name='cars[]' multiple>
        <option value='VW'>VW</option>
        <option value='Hyundai'>Hyundai</option>
        <option value='Ford'>Ford</option>
        <option value='Lexus'>Lexus</option>
    </select>
    <input type='submit'>
</form>
<?php
    echo "GET data: <br>";
    foreach ($_GET as $name => $value)
        if (gettype($value) == 'array') {
            echo $name . '=';
            for ($i = 0; $i < count($value); $i++)
                echo $value[$i] . ' ';
            echo '<br>';
        }
        else
            echo $name . '=' . $value . '<br>';
?>
```
  - Trial 12: Let's try the form in the above example. What if [] is omitted?
    <??? ???='//cs.tru.ca/~mlee/comp3540/Software/test_display_inputs.php' target='try12-iframe'> <select ???='???' ???> <option value='VW'>VW</option> <??? ???='Hyundai'>Hyundai</option> <??? ???='Ford'>Ford</option> <??? ???='Lexus'>Lexus</option> </select> <input ???='???'>  </form>

Some review questions and learning outcomes
- Understand what receives the URL from the client and executes the PHP code specified by the URL?
- What happens to the PHP code after the code is executed?
- Use of PHP for computer programming.
- Use of superglobal variables.
- Use of associative arrays with the 'foreach' loop.
- How to receive data from the client using the HTTP get and post methods?
- How to send data to the client from the client?
- How to display a message sent from the client?