Echo : Prints in PHP
```
<?php echo "Hello World!"; ?>
```
Comments : Commets are used to make the code more understandable for programmer, they are not executed by compiler or interpreter in PHP
```
// One Liner - This is a singleline comment
# Another type of singleline comment

/* Multiline - 
This is a multiline comment */
```
Vardump : This function dumps information about one or more variables in PHP
```
<?php var_dump(var1, var2, ...); ?>
```
Variables : Variables are "containers" for storing information in PHP
```
<?php $Title = "PHP Cheat Sheet By CodeWithHarry"; ?>
```

Data Types : Datatype is a type of data in PHP

<?php $x = "Harry"; echo $x; ?>// String
<?php $x = 1234; var_dump($x); ?> // Integer
<?php $x = 1.2345; var_dump($x); ?> // Float
<?php $names = array("Harry","Rohan","Shubham"); var_dump($names);?> // Array

Class and Objects : A class is a template for objects and an object is an instance of the class in PHP

<?php class Bike { 
  public $color; 
  public $model; 
  public function __construct($color, $model) { 
    $this->color = $color; 
    $this->model = $model; 
  } 
  public function message() { 
    return "My bike is a " . $this->color . " " . $this->model . "!"; 
  } 
} 

$myBike = new Bike("red", "Honda"); 
echo $myBike -> message(); ?>

Escape Characters : Escape sequences are used for escaping a character during string parsing. It is also used for giving special meaning to represent line breaks, tabs, alerts and more in PHP
```
# Line feed
\n
# Carriage return
\r
# Horizontal tab
\t
# Vertical tab
\v
# Escape
\e
# Form feed
\f
# Backslash
\\
# Dollar sign
\$
# Single quote
\'
# Double quote
\"
```

Arithmetic Operators :

# Addition
$x + $y 
# Subtraction
$x - $y
# Multiplication
$x * $y
# Division
$x / $y
# Modulus
$x % $y
# Exponentiation
$x ** $y

PHP Assignment Operators : The PHP assignment operators are used with numeric values to write a value to a variable.

# The left operand gets set to the value of the expression on the right
x = y
# Addition
x += y
x = x + y
# Subtraction
x -= y
x = x - y
# Multiplication
x *= y
x = x * y
# Division
x /= y
x = x / y
# Modulus
x %= y
x = x % y

PHP Comparison Operators :

# Equal - Returns true if $x is equal to $y
$x == $y
# Identical - Returns true if $x is equal to $y, and they are of the same type
$x === $y
# Not equal - Returns true if $x is not equal to $y
$x != $y
# Not equal - Returns true if $x is not equal to $y
$x <> $y
# Not identical - Returns true if $x is not equal to $y, or they are not of the same type
$x !== $y
# Greater than - Returns true if $x is greater than $y
$x > $y
# Less than - Returns true if $x is less than $y
$x < $y
# Greater than or equal to - Returns true if $x is greater than or equal to $y
$x >= $y
# Less than or equal to - Returns true if $x is less than or equal to $y
$x <= $y

PHP Increment / Decrement Operators :

# 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
$x--

PHP Logical Operators :

# And - True if both $x and $y are true
$x and $y
# Or - True if either $x or $y is true
$x or $y
# Xor - True if either $x or $y is true, but not both
$x xor $y
# And - True if both $x and $y are true
$x && $y
# Or - True if either $x or $y is true
$x || $y
# Not - True if $x is not true
!$x

PHP String Operators :

# Concatenation - Concatenation of $txt1 and $txt2
$txt1 . $txt2
# Concatenation assignment - Appends $txt2 to $txt1
$txt1 .= $txt2

PHP Array Operators :

# Union - Union of $x and $y
$x + $y
# Equality - Returns true if $x and $y have the same key/value pairs
$x == $y
# Identity - Returns true if $x and $y have the same key/value pairs in the same order and of the same types
$x === $y
# Inequality - Returns true if $x is not equal to $y
$x != $y
# Inequality - Returns true if $x is not equal to $y
$x <> $y
# Non-identity - Returns true if $x is not identical to $y
$x !== $y

PHP Conditional Assignment Operators :

# Ternary - Returns the value of $x. The value of $x is expr2 if expr1 = TRUE. The value of $x is expr3 if expr1 = FALSE
$x = expr1 ? expr2 : expr3

Conditional Statements :

# If Statement - if statement checks the condition and if it is True, then the block of if statement executes; otherwise, control skips that block of code.
if (condition) { 
// code to execute if condition is met 
}
# If..Else - if the condition of if block evaluates to True, then if block executes otherwise else block executes
if (condition) { 
// code to execute if condition is met 
} else { 
// code to execute if condition is not met 
}
# If..Elseif..Else - It executes different codes for more than two conditions
if (condition) { 
// code to execute if condition is met 
} elseif (condition) { 
// code to execute if this condition is met 
} else { 
// code to execute if none of the conditions are met 
}

Switch Case Statements : It allows a variable to be tested for equality against a list of values (cases).

switch (n) { 
    case x: 
    // code to execute if n=x; 
    break; 
    case y: 
    // code to execute if n=y; 
    break; 
    case z: 
    // code to execute if n=z; 
    break; 
    // add more cases as needed 
    default: 
    //code to execute if n is neither of the above; 
}

For Loop : It is used to iterate the statements several times. It is frequently used to traverse the data structures like the array and linked list.
```
for ($i=0 ; $i < = 10 ; $i++) { 
    // code to execute goes here 
}
```
Foreach Loop : The foreach loop loops through a block of code for each element in an array.
```
foreach ($InsertYourArrayName as $value) { 
    // code to execute goes here 
}
```
While Loop : It iterate the block of code as long as a specified condition is True or vice versa.
```
while ($i < 10) { 
    // code to execute goes here 
}
```
Do-While Loop : This loop is very similar to the while loop with one difference, i.e., the body of the do-while loop is executed at least once even if the condition is False. It is an exit-controlled loop.
```
do { 
    // code to execute goes here; 
} while (condition);
```

Predefined Variables

$GLOBALS : $GLOBALS is a PHP super global variable which is used to access global variables from anywhere in the PHP script.

<?php 
$a = 10; 
$b = 15; 

function addition() { 
    $GLOBALS['c'] = $GLOBALS['a'] + $GLOBALS['b']; 
} 

addition(); 
echo $c; 
?>

$_SERVER :

# Returns the filename of the currently executing script. $_SERVER is a PHP super global variable which holds information about headers, paths, and script locations.
$_SERVER['PHP_SELF']
# Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER['GATEWAY_INTERFACE']
# Returns the IP address of the host server
$_SERVER['SERVER_ADDR']
# Returns the name of the host server (such as www.codewithharry.com)
$_SERVER['SERVER_NAME']
# Returns the server identification string (such as Apache/2.2.24)
$_SERVER['SERVER_SOFTWARE']
# Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER['SERVER_PROTOCOL']
# Returns the request method used to access the page (such as POST)
$_SERVER['REQUEST_METHOD']
# Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER['REQUEST_TIME']
# Returns the query string if the page is accessed via a query string
$_SERVER['QUERY_STRING']
# Returns the Accept header from the current request
$_SERVER['HTTP_ACCEPT']
# Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER['HTTP_ACCEPT_CHARSET']
# Returns the Host header from the current request
$_SERVER['HTTP_HOST']
# Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER['HTTP_REFERER']
# Is the script queried through a secure HTTP protocol?
$_SERVER['HTTPS']
# Returns the IP address from where the user is viewing the current page
$_SERVER['REMOTE_ADDR']
# Returns the Hostname from where the user is viewing the current page
$_SERVER['REMOTE_HOST']
# Returns the port being used on the user's machine to communicate with the web server
$_SERVER['REMOTE_PORT']
# Returns the absolute pathname of the currently executing script
$_SERVER['SCRIPT_FILENAME']
# Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as someone@codewithharry.com)
$_SERVER['SERVER_ADMIN']
# Returns the port on the server machine being used by the webserver for communication (such as 80)
$_SERVER['SERVER_PORT']
# Returns the server version and virtual hostname which are added to server-generated pages
$_SERVER['SERVER_SIGNATURE']
# Returns the file system based path to the current script
$_SERVER['PATH_TRANSLATED']
# Returns the path of the current script
$_SERVER['SCRIPT_NAME']
# Returns the URI of the current page
$_SERVER['SCRIPT_URI']

$_GET : PHP $_GET is a PHP super global variable which is used to collect form data after submitting an HTML form with method="get".
```
<?php 
    echo "Hello" . $_GET['Example'] . " at " . $_GET['web']; 
?>
```

$_POST : PHP $_POST is a PHP super global variable which is used to collect form data after submitting an HTML form with method="post". $_POST is also widely used to pass variables.

<html>
<body>
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
Name: <input type="text" name="fname">
<input type="submit">
</form>
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_POST['fname'];
    if (empty($name)) {
        echo "Please Enter your name";
    } else {
        echo $name;
    }
}
?>
</body>
</html>

$_REQUEST : PHP $_REQUEST is a PHP super global variable which is used to collect data after submitting an HTML form.

<html>
<body>
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
Name: <input type="text" name="fname">
<input type="submit">
</form>
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_REQUEST['fname'];
    if (empty($name)) {
        echo "Please Enter your name";
    } else {
        echo $name;
    }
}
?>
</body>
</html>

Variable-handling Functions

boolval : Boolval is used to get the boolean value of a variable.

<?php
echo '0: '.(boolval(0) ? 'true' : 'false')."\n"; 
echo '42: '.(boolval(42) ? 'true' : 'false')."\n"; 
echo '0.0: '.(boolval(0.0) ? 'true' : 'false')."\n"; 
echo '4.2: '.(boolval(4.2) ? 'true' : 'false')."\n"; 
echo '"": '.(boolval("") ? 'true' : 'false')."\n"; 
echo '"string": '.(boolval("string") ? 'true' : 'false')."\n"; 
echo '"0": '.(boolval("0") ? 'true' : 'false')."\n"; 
echo '"1": '.(boolval("1") ? 'true' : 'false')."\n"; 
echo '[1, 2]: '.(boolval([1, 2]) ? 'true' : 'false')."\n"; 
echo '[]: '.(boolval([]) ? 'true' : 'false')."\n"; 
echo 'stdClass: '.(boolval(new stdClass) ? 'true' : 'false')."\n"; 
?>

isset : It is used to check whether a variable is empty. It also checks whether the variable is set/declared:
```
<?php
$x = 0; 
// True because $x is set 
if (isset($x)) { 
    echo "Variable 'x' is set"; 
} 
?>
```

unset : It unsets variables.

<?php
$a = "Namaste world!"; 
echo "The value of 'a' before unset: " . $a ; 
unset($a); 
echo "The value of 'a' after unset: " . $a; 
?>

debug_zval_dump : debug_zval_dump is used to dump a string representation of an internal zval structure to output.
```
<?php
$var1 = 'Hello'; 
$var1 .= ' World'; 
$var2 = $var1; 
debug_zval_dump($var1); 
?>
```
debug_zval_dump : debug_zval_dump is used to dump a string representation of an internal zval structure to output.
```
<?php
$var1 = 'Hello'; 
$var1 .= ' World'; 
$var2 = $var1; 
debug_zval_dump($var1); 
?>
```

empty : Empty is used to check whether a variable is empty or not.

<?php
$var = 0; 
// Evaluates to true because $var is empty 
if (empty($var)) { 
    echo '$var is either 0, empty, or not set at all'; 
} 
// Evaluates as true because $var is set 
if (isset($var)) { 
    echo '$var is set even though it is empty'; 
} 
?>

floatval : It returns the float value of different variables:

<?php
$var = '122.34343The'; 
$float_value_of_var = floatval($var); 
echo $float_value_of_var; // 122.34343 
?>

get_defined_vars : It returns all defined variables, as an array:

<?php
$b = array(1, 1, 2, 3, 5, 8); 
$arr = get_defined_vars(); 
// print $b 
print_r($arr["b"]); 
/* print path to the PHP interpreter (if used as a CGI) 
* e.g. /usr/local/bin/php */ 
echo $arr["_"]; 
// print the command-line parameters if any 
print_r($arr["argv"]); 
// print all the server vars 
print_r($arr["_SERVER"]); 
// print all the available keys for the arrays of variables 
print_r(array_keys(get_defined_vars()));
?>

get_resource_type : It returns the resource type:

<?php
// prints: stream 
$fp = fopen("foo", "w"); 
echo get_resource_type($fp) . "\n"; 
// prints: curl 
$c = curl_init (); 
echo get_resource_type($c) . "\n"; // works prior to PHP 8.0.0 as since 8.0 curl_init returns a CurlHandle object
?>

gettype : It returns the type of different variables:
```
<?php
$a = 3; 
echo gettype($a) ; 
?>
```
intval : It returns the integer value of different variables:
```
<?php
echo intval(42);
?>
```
is_array : To check whether a variable is an array or not:
```
<?php
$a = "Hello"; 
echo "a is " . is_array($a) ;
?>
```

Array : An array stores multiple values in one single variable.

<?php
$cms = array("Harry", "Lovish", "Rohan");
echo "Who needs chocolate? Is it" . $cms[0] . ", " .
$cms[1] . " or " . $cms[2] . "?";
?>

Functions : A function is a block of statements that can be used repeatedly in a program
```
<?php
function NameOfTheFunction() { 
    //place PHP code here 
}
?>
```

MySQLi Functions : These functions allow you to access MySQL database server.

<?php
# mysqli_connect() Function - It opens a non-persistent MySQL connection
mysqli_connect()
# mysqli_affected_rows() Function - It returns the number of affected rows
mysqli_affected_rows()
# mysqli_connect_error() Function - It shows the Error description for the connection error
mysqli_connect_error()
# mysqli_fetch_all() Function - It fetches all result rows as an array
mysqli_fetch_all()
# mysqli_fetch_array() Function - It fetches a result row as an associative, a numeric array, or both
mysqli_fetch_array()
# mysqli_fetch_assoc() Function - It fetches a result row as an associative array
mysqli_fetch_assoc()
# mysqli_fetch_row() Function - It fetches one row from a result set and returns it as an enumerated array
mysqli_fetch_row()
# mysqli_kill() Function - It kills a MySQL thread
mysqli_kill()
# mysqli_close() Function - It closes a database connection
mysqli_close()
?>

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