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PHP-SyntaxGuide.md

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PHP Cheatsheet

INTRO

  • PHP: Hypertext Preprocessor
  • created by Rasmus Lerdorf in 1994
  • executed on server and sent to browser as plain HTML

FUNCTIONALITY

  • generate pages/files dynamically
  • access files on a server
  • collect data from web forms
  • send emails
  • track web traffic with cookies
  • restrict access to website
  • encrypt data

SCRIPT

  • use semicolons to end line ;

  • Case sensitivity $color $Color $COLOR (all treated as separate variables) BUT keywords, function and classes names are case-insensitive

  • Comments // This is a single line comment # This is also a single line comment

VARIABLES

  • dont need to be declared before adding a value to them (php automatically assigns correct data type) CASE SENSITIVE

      <?php
  
      $var_name = value;
      
  ?>

CONSTANTS

  • value cannot be changed after it is set
  • do not need a leading dollar sign ($)
  • can be accessed regardless of scope
  • values can only be strings and numbers

eg. database username and password, website's base URL, company name, etc.

    <?php
        // Defining constant
        define("USER_EMAIL", "[email protected]");
        
        // Using constant
        echo 'User email is - ' . USER_EMAIL;
    ?>

ECHO & PRINT

Almost the same! Both can display anything that can be displayed to the browser, such as string, numbers, variables values, the results of expressions etc.

    <?php
        echo "has no return value, can take multiple parameters";

        print "can only take one argument, and always returns 1 print";
    ?>

DATA TYPES

String

    <?php 
        "Hello World";
    ?>

Integer

    <?php
        $integer = 5985;
    ?>

Float (floating point numbers - also called double)

    <?php
      $float = 10.365;
    ?>

Boolean

    <?php
        $var1 = true;   
        $var2 = false;
    ?>

Array

    <?php
        $beerTypes = array("lager","IPA","saison");
    ?>

Object

        <?php
            class Pet {
                Pulic $species;
                public $color;
                public $size;
                public function __construct($color, $size) {
                    $this->color = $color;
                    $this->model = $size;
                }
                public function message() {
                    return "My pet is a " $this->species "and is " . $this->color . " and" . $this->size . "!";
            }
        }

                $myPet = new Pet("armadillo", "brown", "small");
                    echo $myPet -> message();
                    echo "<br>";

                $myPet = new Pet("feral cat", "calico", "large");
                        
        ?>

NULL

        <?php
            $message = "Hello world!";
            $message = null;
            var_dump($message);
        ?>

OPERATORS

groups:

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Increment/Decrement operators
  5. Logical operators
  6. String operators
  7. Array operators
  8. Conditional assignment operators

Examples Arithmetic

Operator Description Example
+ Addition $x + $y
- Subtraction $x - $y
* Multiplication $x * $y
/ Division $x / $y
% Modulus $x % $y
* Multiplication $x * $y

Examples Assignment

Operator Description Example
= Assign $x = $y
+= Add and assign $x += $y
-= Subtract and assign $x -= $y
*= Multiply and assign $x *= $y
/= Divide and assign quotient $x /= $y
%= Divide and assign modulus $x %= $y

Examples Comparison

Operator Description Example
== Equal $x == $y
=== Identical $x === $y
!= Not equal $x != $y
<> Not equal $x <> $y
!== Not identical $x !== $y
< Less than $x < $y
> Greater than $x > $y
>= Greater than or equal to $x >= $y
<= Less than or equal to $x <= $y

Examples Incrementing and Decrementing

Operator Description Effect
++$x Pre-increment Increments $x by one, then returns $x
$x++ Post-increment Returns $x, then increments $x by one
--$x Pre-decrement Decrements $x by one, then returns $x
$x-- Post-decrement Returns $x, then decrements $x by one

Examples Logical

Operator Description Example
and And $x and $y
or Or $x or $y
xor Xor $x xor $y
&& And $x && $y
! Not !$x

Examples String

Operator Description Example
. Concatenation $str1 . $str2
.= Concatenation assignment $str1 .= $str2

Examples Array

Operator Description Example
+ Union $x + $y
== Equality $x == $y
=== Identity $x === $y
!= Inequality $x != $y
<> Inequality $x <> $y
!== Non-identity $x !== $y

CONDITIONAL STATEMENTS: IF & ELSE & ELSEIF

  <?php
    $age = 17;
    //$age=(int)readline("enter age: ");

        if ($age>19){
            echo "User is 19 or older" . "<br>";
        }
        else{
            echo "User is under 19" . "<br>";
        }
    ?>

FUNCTIONS

    <?php
        // Defining function

        function registrationMessage(){
            echo "Your registration was successful!";
        }

        // Calling function
        registrationMessage()
    ?>


   <?php

        $miles = 35;

        function convertMilestoKM($miles){
            $output = $miles * 1.609344;

            echo $miles . " miles equals " . $output . " kilometers"; 
        }

            convertMilestoKM($miles);
    
    ?>

ARRAYS

Types:

Indexed array — An array with a numeric key.

        <?php
            $apples = array("gala", "fuji", "McIntosh");
        ?>

Associative array — An array where each key has its own specific value.

        <?php
            $heightInFeet = array("Shrek"=> 8, "donkey"=> 4, "Fiona"=> 5.10, "Lord Farquad"=>4.6);
            
             var_dump ($heightInFeet);
        ?>

Multidimensional array — An array containing one or more arrays within itself.

        <?php

          $guests = array(
              array(
                  "name" => "Shrek",
                  "age" => "400",
              ),
              array(
                  "name" => "Fiona",
                  "age" => "30",
              ),
              array(
                  "name" => "Lord Farquad",
                  "age" => "569",
              )
          );
   
           echo "Shrek is " . $guests[0]["age"] . " years old.";
        ?>

LOOPS

while loops:

    <?php
        $i = 20;                                        //start countdown at 20

        while($i > 0) {                                 //while i is greater than 0
            $i--;                                       //decrement
            echo "The countdown is at " . $i . "<br>";
        }
    ?>

for loops:

   <?php
        //Write a program to count backwards from 20 that stops at 0
        
        function backFromTwenty(){
        
            for($i=20; $i>=0; $i--){
                echo $i . " ";
                }
            }
            backFromTwenty()
    ?>