<?php
$i = "World!";
echo "Hello " . $i;
?>

<?php
// One liner
# another one liner
/* This is
a multiline
comment */
?>

function sayHello() {
    echo "Hello!";
}
sayHello(); // Outputs: Hello!

$i = 1;
$pi = 3.14;
$stringName = "value";
$names = array("John", "Jane", "Jack");
var_dump($names);

$a = array(1, 2, array("a", "b", "c"));
var_dump($a);

class foo {
   function do_foo() {
     echo "Doing foo.";
    }
 }
$bar = new foo;
$bar->do_foo();

echo "\n"; //New line

Line feed	\n
Carriage return	\r
Horizontal tab space	\t
Vertical tab	\v
Escape characters	\e
Form (page or section separator)	\f
Backslash	\\
Dollar sign	\$
Single quote	\'
Double quote	\"

// For loop count to 10
for( $i = 0; $i < 10; $i += 1) {
    echo $i . "\n";
}

// Declare an array
$arr = array("tesla", "bmw", "audi");
// Loop through the array elements
foreach ($arr as $element) {
    echo "$element ";
}

// Declare a number
$i = 10;
// Counting down to 0
while ($i >= 0) {
  echo $i . "\n";
  $i--;
}

$i = 10;
// Counting back to 0
do {
    echo $i . "\n";
    $i--;
} while ($i >= 0);

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

x = y	x = y
x += y	x = x + y
x -= y	x = x - y
x *= y	x = x * y
x /= y	x = x / y
x %= y	x = x % y

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

++$x	Pre-increment
$x++	Post-increment
--$x	Pre-decrement
$x--	Post-decrement

!$x	Not
$x and $y / $x && $y	And
$x or $y / $x || $y	Or
$x xor $y	Xor

$s1 . $s2	Concatenation
$s1 .= $s2	Concatenation assignment

if (condition) {
// execute this if condition is true
}

if (condition) {
  // do this if condition is true
} else {
  // do this if condition is false
}

if (condition) {
  // code if condition is true
} elseif (condition2) {
  // condition is false and condition2 is true
} else {
  // if none of the conditions are met
}

switch (n) {
case a:
  //code to execute if n=a;
break;
case b:
  //code to execute if n=b;
break;
case c:
  //code to execute if n=c;
break;
  // more cases as needed
default:
  // if n is neither of the above;
}

$result = condition ? value1 : value2;

Is the same as:

if (condition) {
    $result = value1;
} else {
    $result = value2;
}

function greet($name) {
    echo "Hello " . $name;
}
greet("John");
// Outputs: Hello John

function greet($name = "Visitor") {
    echo "Hello, " . $name;
}
greet(); // Outputs: Hello, Visitor

function add($a, $b) {
    return $a + $b;
}
$result = add(3, 5);
// $result is 8

$number = 10;
function multiplyByTwo() {
    global $number;
    $number *= 2;
}
multiplyByTwo();
echo $number; // Outputs: 20

$greet = function($name) {
    echo "Hello, " . $name;
};
$greet("Alice"); // Outputs: Hello, Alice

• String: strlen(), str_replace(), substr()
• Array: array_merge(), array_pop(), array_keys()
• Math: abs(), ceil(), floor()
• Date: date(), strtotime(), mktime()
• File: fopen(), fwrite(), fread()

$colors = array("Red", "Green", "Blue");
echo $colors[0]; // Outputs: Red

$age = array("Peter" => 35, "Ben" => 37, "Joe" => 43);
echo $age['Peter']; // Outputs: 35

$students = array(
  "John" => array("Math" => 123, "Science" => 456),
  "Jane" => array("Math" => 789, "Science" => 987)
);
echo $students['John']['Math']; // Outputs: 123

$a = 5;
$b = 10;
function addition() {
  $GLOBALS['sum'] = $GLOBALS['a'] + $GLOBALS['b'];
}
addition();
echo $sum;

// URL: html6.com?x=1&y=2
$x = $_GET['x'];  // $x will be 1

$username = $_POST['username'];
// Variable will contain the value entered in the form

<form method="post" action="form.php">
  <input type="text" name="username">
   <input type="submit">
</form>

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $username = $_REQUEST['username'];
    echo "Hello, " . htmlspecialchars($username);
}

• htmlspecialchars(): Converts special characters to HTML entities
• trim(): Removes whitespace from beginning and end of a string
• stripslashes(): Removes backslashes from a string

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $input = htmlspecialchars($_POST['input_field'], ENT_QUOTES, 'UTF-8');
    $input = trim($input);
    if (get_magic_quotes_gpc()) {
        $input = stripslashes($input);
    }
}

input	boolval(input)
0	false
12	true
0.0	false
1.2	true
""	false
"hello"	true
"0"	false
"1"	true
[1, 2]	true
[]	false
new stdClass	true

$x = 0;
if (isset($x)) {
echo "x is set";
}
// True because $x is set

$x = "Hello world!";
echo "before unset: " . $x;
unset($x);
echo "after unset: " . $a;
// Throws warning for undefined variable

input	empty(input)
""	true
0	true
"php"	false

$variable	gettype($variable)
12	integer
12.3	double
"HTML Cheat Sheet"	string
array(1, 2, 3)	array
fopen("file.txt", "r")	resource

$variable	intval($variable)
12	12
12.3	12
"12.3"	12
"Hello"	0

To check whether a given variable is an array

$mysqli = new mysqli("localhost", "username", "password", "database");
if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

$result = $mysqli->query("SELECT * FROM table_name");
if ($result) {
    while ($row = $result->fetch_assoc()) {
        echo $row["column_name"];
    }
}

$stmt = $mysqli->prepare("SELECT * FROM table_name WHERE column_name = ?");
$stmt->bind_param("s", $value);
$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    echo $row["column_name"];
}
$stmt->close();

$sql = "INSERT INTO table_name (column1, column2) VALUES ('value1', 'value2')";
if ($mysqli->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $mysqli->error;
}

$sql = "UPDATE table_name SET column1 = 'value' WHERE condition";
if ($mysqli->query($sql) === TRUE) {
    echo "Record updated successfully";
} else {
    echo "Error: " . $sql . "<br>" . $mysqli->error;
}

$sql = "DELETE FROM table_name WHERE condition";
if ($mysqli->query($sql) === TRUE) {
    echo "Record deleted successfully";
} else {
    echo "Error: " . $sql . "<br>" . $mysqli->error;
}

$mysqli->close();

$email = "admin@htmlcheatsheet.com";
if (preg_match('/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/', $email)) {
    echo "Valid email address";
} else {
    echo "Invalid email";
}

• preg_match() - Returns 1 if the pattern was found
• preg_match_all() - Returns the number of times the pattern was found
• preg_replace() - Returns a new string where matched patterns have been replaced

• i - Performs a case-insensitive search
• m - Performs a multiline search
• u - Enables correct matching of UTF-8 encoded patterns

• [abc] - Find one character from the options between the brackets
• [^abc] - Find any character NOT between the brackets
• [0-9] - Find one character from the range 0 to 9

• | - Find a match for any one of the patterns separated by |
• . - Find just one instance of any character
• ^ - Finds a match as the beginning of a string
• $ - Finds a match at the end of the string
• \d - Find a digit
• \s - Find a whitespace character
• \b - Find a match at the beginning or end of a word
• \uxxxx - Find the Unicode character specified by the hexadecimal number xxxx

• n+ - Contains at least one n
• n* - Contains zero or more occurrences of n
• n? - Contains zero or one occurrences of n
• n{x} - Contains a sequence of X n's
• n{x,y} - Contains a sequence of X to Y n's
• n{x,} - Contains a sequence of at least X n's

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $filters = array(
        'email' => FILTER_VALIDATE_EMAIL,
    );
    $sanitized_inputs = filter_input_array(INPUT_POST, $filters);
    if ($sanitized_inputs['email'] === false) {
        echo "Invalid email address!";
    } else {
        $email = $sanitized_inputs['email'];
        echo "Valid email address: " . $email;
    }
}

• filter_has_var() - Check if a variable of the specified type exists
• filter_id() - Returns the ID belonging to a named filter
• filter_input() - Retrieves a specified external variable by name
• filter_input_array() - Pulls external variables and optionally filters them
• filter_list() - Returns a list of all supported filters
• filter_var_array() - Gets multiple variables and optionally filters them
• filter_var() - Filters a variable with a specified filter

• FILTER_VALIDATE_BOOLEAN - Validates a boolean
• FILTER_VALIDATE_EMAIL - Certifies an e-mail address
• FILTER_VALIDATE_FLOAT - Confirms a float
• FILTER_VALIDATE_INT - Verifies an integer
• FILTER_VALIDATE_IP - Validates an IP address
• FILTER_VALIDATE_REGEXP - Confirms a regular expression
• FILTER_VALIDATE_URL - Validates a URL
• FILTER_SANITIZE_EMAIL - Removes all illegal characters from an e-mail
• FILTER_SANITIZE_ENCODED - Removes/Encodes special characters
• FILTER_SANITIZE_MAGIC_QUOTES - Applies addslashes()
• FILTER_SANITIZE_NUMBER_FLOAT - Removes all characters except digits, +- and .,eE
• FILTER_SANITIZE_NUMBER_INT - Removes all characters except digits and + -
• FILTER_SANITIZE_SPECIAL_CHARS - Removes special characters
• FILTER_SANITIZE_FULL_SPECIAL_CHARS - Converts special characters to HTML entities
• FILTER_SANITIZE_STRING - Removes tags/special characters from a string
• FILTER_SANITIZE_URL - Removes all illegal characters from a URL
• FILTER_UNSAFE_RAW - Do nothing, optionally strip/encode special characters
• FILTER_CALLBACK - Call a user-defined function to filter data

// Get current timestamp
$currentTimestamp = time();
// Format and display current date and time
echo "Current timestamp: " . $currentTimestamp . "<br>";
// Format date using date() function
echo "Current date: " . date("Y-m-d") . "<br>";
echo "Current time: " . date("H:i:s") . "<br>";
// Format date and time with specific timezone
date_default_timezone_set('America/New_York');
echo "Current date and time in New York: " . date("Y-m-d H:i:s");

• d - Days from 01 to 31
• j - Days 1 to 31
• D - Mon through Sun
• l - Sunday through Saturday
• N - 1 (Mon) through 7 (Sat)
• w - 0 (Sun) through 6 (Sat)
• m - Months, 01 through 12
• n - Months, 1 through 12
• F - January through December
• M - Jan through Dec
• Y - Four digits year (e.g. 2018)
• y - Two digits year (e.g. 18)
• L - Defines whether it's a leap year (1 or 0)
• a - am and pm
• A - AM and PM
• g - Hours 1 through 12
• h - Hours 01 through 12
• G - Hours 0 through 23
• H - Hours 00 through 23
• i - Minutes 00 to 59
• s - Seconds 00 to 59

• Don't forget the semicolon!
• Mismatched brackets ()
• Incorrect quotes: " '
• Undefined variables
• Case sensitivity $Var ≠ $var
• Incorrect function calls that does not exist or with incorrect parameters

Using include or require with an incorrect file path. Use absolute paths or ensure relative paths are correct.

Failing to sanitize user inputs can lead to SQL injection attacks. Use prepared statements and parameterized queries.

Use try-catch blocks and implementing proper error handling mechanisms.

Check if array keys exist before accessing them.

Start sessions with session_start() and handle session variables correctly.

Unintentional output before headers are sent can cause "headers already sent" errors. Use output buffering or ensure no output before header() calls.

Variable scope misunderstandings. Use global keyword or pass variables as function arguments.

Incorrect settings in the php.ini file can lead to various issues.

Using deprecated functions or features that may be removed in future PHP versions.

Set the default timezone using date_default_timezone_set().

Increase memory limit in php.ini or optimize code to use less memory.

• Use Error Reporting: Enable error reporting during development
• Code Reviews: Regular code reviews can catch errors early
• Testing: Write unit tests and integration tests
• Documentation: Keep your code well-documented
• Stay Updated: Keep up with the latest PHP versions and best practices