PHP

(PHP: hypertext preprocessor)

Facts:

• The first word of the acronym is an acronym, recursive backronym, originally the acronym stood for Personal Home Page
• Developed in 1994
• PHP is a server scripting language. It can send emails, process a contact form, or connect to a database. HTML, CSS, JS are run on web browser, and we can not use them to store the user info permanently, because the browser gets closed down and we want a way to store that data somewhere centrally so that user can access it anywhere on the web.

(HTML...CSS...JS...WebGL)Web Browser <---->internet<----->Web Server (PHP...MySQL, Apache, Server Modules)

So languages that work on the web server allow us to do the web service-specific things like logging a user in or returning their tweets or saving their progress in a game.

• PHP is powering 81.8% of the web as of 2021.
• It's a language in which WP is built and learning PHP will enable you to create WP plug ins, customize WP themes and etc.
• .php file can contain HTML, CSS, JS and PHP code.

Tips:

How to display error messages in PHP (if you forged " or smth else)

• create a separate new file, call it php.ini, it will contain initialization options

• set 2 variables

• error_reporting = E_ALL

• meaning report on any type of errors and

• display_errors = On

• these will allow displaying errors when we develop site. If it's online, need to delete them so the hackers won't use the error messages to access your website.

• if error message refers to line 6, the error may be on previous line, because the error was not detected until line 6.

• echo "Hello World"; --> displays text in php. Use only semi columns.

• must put HTML outside of these tags

<?php 
some php code here
?>

Variables

String variables (containing a string of characters) in PHP

<?php
$name = "Rob";
?>

example:

<?php
$name = "Rob";
echo "My name is $name";
?>

It will display variable value -->

my name is Rob

<?php
$name = "Rob";
echo $name;
?>

it will display -->

Rob

• How to put strings together (Concatenating)

$string1 = "This is the 1st part of a sentence";
$string2 = "here you have the 2nd one";
echo $string1.$string2;

." ". is used to put a space between strings

you can put HTML inside those strings to make them appear on different lines. Add <p> tag.

$string1 = "<p>This is the 1st part of a sentence</p>";
$string2 = "<p>here you have the 2nd one</p>";
echo $string1." ".$string2;

• PHP Variables containing a string of numbers

$myNumber = 45;
$calculation = $myNumber * 31 / 97 + 4;
echo $calculation;

it will display -->

18.381443298969

for multiplication use asterisk (*)

$myNumber = 45;
$calculation = $myNumber * 31 / 97 + 4;
echo "The result of the calculation is ".$calculation;

• Boolean variables in PHP

$myBool = true;
echo "<p>This statement is true? ".$myBool."</p>";

It will show -->

1

$myBool = false;
echo "<p>This statement is true? ".$myBool."</p>";  

It will show -->

0 or nothing

Note: it doesn't give true false, but 1 or 0. This is how PHP treats true and false.

• Store Variable names within variables:

$name = "Mari";
$variableName = "name";
echo $$variableName;

Arrays

Arrays (ways of storing a number of different values in the same object) in PHP

$myArray = array("a", "b", "c", "d");
print_r($myArray);
shows -->

Array ( [0] => a [1] => b [2] => c [3] => d )

print_r shows the contents of the array (_r stands for readable)

In the page source, it displays like -->

Array
( 
   [0] => a 
   [1] => b 
   [2] => c 
   [3] => d
)

• Get items from Array

echo $myArray[1];

displays b

• Define an array by creating values manually:

the arrays are associative, meaning you can put anything you like in the index, e.g. jump from 2 to 5 or call it "myFavouriteFood"

$anotherArray[0] = "a";
$anotherArray[2] = "b";
$anotherArray["myFavouriteFood"] = "ice cream";
print_r($anotherArray);

• Putting line breaks:

echo "<br><br>";

• If you want to make an associative PHP array like "myFavouriteFood" to store info about password, username, etc, then:

$thirdArray = array("France" => "French", "USA" => "English");
print_r($thirdArray);

Shows --> Array ( [France] => French [USA] => English )

• Get the length of the array (number of items in the array)

echo sizeof($thirdArray);

Shows --> 2

• Add an item to the end of an array

$myArray = array("a", "b", "c", "d");
$myArray[] = "e";
print_r($myArray);

• Remove item using unset command

$myArray = array("a", "b", "c", "d");
unset($myArray["0"]);
print_r($myArray);

Shows -->

Array 
( 
   [1] => b 
   [2] => c 
   [3] => d 
)

If statements

$user = "rob";
if ($user == "rob") {
    echo "Hi Rob!";
}   else {
    echo "I don't know you";
}

$age = 25;
if ($age >= 18 || $user == "rob" ) {
    echo "you may proceed..";
} else {
    echo "You're too young, sorry!";
}

Note: || means OR

Loops

For loops

When Gmail is showing all of your emails that's a loop because it's looping all the emails and displays them for you.

for loop var counter variable i counter variable name i = 0 setting i to its initial value

for ($i = 0; $i < 10; $i++) {
      echo #i."<br>";
}

it will display 0 1 2 3 4 5 6 7 8 9

for ($i = 2; $i <= 30; $i = $i + 2) {
      echo #i."<br>";
}

it will display 2 4 6 8 10 12 14 up to 30 including.

for ($i = 10; $i >= 0; $i--) {
      echo #i."<br>";
}

It will display 10 9 8 7 6 5 4 3 2 1 0

Looping through arrays

$family = array("rob", "Tommy", "M");

for ($i = 0; $i < sizeof($family); $i++) {      
    echo $family[$i]."<br>";
}

It will display --> rob Tommy M 2nd method is foreach loop

foreach ($family as $key => $value) {
      echo "Array item ".$key." is ".$value."<br>";
}

it will display -->

Array item o is Rob

Array item 1 is Tommy

Array item 2 is M

PHP, While Loops

$i = 0;
while ($i <= 10) {
    echo $i."<br>";
    $i++;
}

It shows 0 1 2 3 4 5 6 7 8 9 10

$i = 5;
while ($i <= 25) {
    echo $i."<br>";
    $i = $i +5;
}

if you use instead of $i++ e.g.

$i = $i +5;

it will increase numbers by 5 and show 5 10 15 20 25 or another way:

$i = 1;
while ($i <= 10) {
    $j = $i * 5
    echo $j."<br>";
    $i++;
}

To present items from the array: 

$family = array ("A", "B");
$i = 0;
while ($i < sizeof($family)) {
echo $family[$i]."<br>";
$i++;
}

It shows items: A B

GET Variables

GET Variables & POST Variables are used to create interaction between user and server.

1. Get variable in the URL string --> /?name=rob&password=1234&gender=male

to access them need to know that they are contained in the $_get. So you need to type

print_r($_GET);

to present a particular value:

echo $_GET("gender")

2. Use a form:

As HTML:

<p>What is you name?</p>
<form>
    <input name="name" type="text">
    <input type="submit" value="Go!">
</form>

For PHP:

echo "Hi there "$_GET['name']."!"

and you get Hi there and any name you input in the form's input field.

• Challenge: Filename: is_it_prime.php

POST Variables

Post Variables are different than GET Variables, because they aren't encoded in URL, so that makes them a bit more secure.

<p>What is you name?</p>
<form method="post">    
    <input name="name" type="text">    
    <input type="submit" value="Go!">
</form>

for PHP -->

print_r($_POST);

If you will want to submit some data twice, you'll get a pop-up telling you to confirm the resumbition.

• Challenge: When a user enters their name program checks to see if the name is on the array of usernames. If so, hello ...name... is shown on the page. Filename: checking_users.php

Mini Projects

1. A Working Contact Form (which validation and email sending)

2. Weather Scraper