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Basic PHP Syntax

A PHP script can be placed anywhere in the document.
A PHP script starts with <?php and ends with ?>
The default file extension for PHP files is " .php ".
A PHP file normally contains HTML tags, and some PHP scripting code.

<!DOCTYPE html> <html> <body> <h1>My first PHP page</h1> <?php echo "Hello World!"; ?> </body> </html>

In PHP, keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are not case-sensitive.

Comments in PHP

A comment in PHP code is a line that is not executed as a part of the program. Its only purpose is to be read by someone who is looking at the code
Comments can be used to:
- Let others understand your code
- Remind yourself of what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code

Examples :

              
      // This is a single-line comment
      # This is also a single-line comment

              
      /*
        This is a multiple-lines comment block
        that spans over multiple
        lines
      */

              
      // You can also use comments to leave out parts of a code line
      $x = 5 /* + 15 */ + 5;
      echo $x;

Output

With PHP, there are two basic ways to get output: echo and print.
The differences are small: echo has no return value while print has a return value of 1 so it can be used in expressions. echo can take multiple parameters (although such usage is rare) while print can take one argument. echo is marginally faster than print.

The echo statement can be used with or without parentheses: echo or echo().

              
    echo "<h2>PHP is Fun!</h2>";
    echo "Hello world!<br>";
    echo "I'm about to learn PHP!<br>";
    echo "This ", "string ", "was ", "made ", "with multiple parameters.";

The print statement can be used with or without parentheses: print or print().

              
    print "<h2>PHP is Fun!</h2>";
    print "Hello world!<br>";
    print "I'm about to learn PHP!";

PHP Variables

Variables are "containers" for storing information.
In PHP, a variable starts with the $ sign, followed by the name of the variable:
$txt = "Hello world!";
Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.
Rules for PHP variables:
- A variable starts with the $ sign, followed by the name of the variable
- A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive ($age and $AGE are two different variables)

Example:

              
    $txt = "simple steps";
    echo "I love " . $txt . "!";
    $x = 5;
    $y = 4;
    echo $x + $y;

PHP Constants

Constants are like variables except that once they are defined they cannot be changed or undefined.
To create a constant, use the define() function.
[ define(name, value, case-insensitive) ]
- name: Specifies the name of the constant
- value: Specifies the value of the constant

Example :

              
  define("GREETING", "Welcome to W3Schools.com!");
  echo GREETING;

PHP Constant Arrays

              
  define("cars", [
    "Alfa Romeo",
    "BMW",
    "Toyota"
  ]);
  echo cars[0];

Constants are Global

              
  define("GREETING", "Welcome to W3Schools.com!");
  function myTest() {
    echo GREETING;
  }
  myTest();

PHP Data Types

Variables can store data of different types, and different data types can do different things.
PHP supports the following data types:
- String
- Integer
- Float
- Boolean
- Array
- Object
- NULL
- Resource
PHP String
A string is a sequence of characters, like "Hello world!".
A string can be any text inside quotes. You can use single or double quotes:
```
              
    $x = "Hello world!";
    $y = 'Hello world!';
              
            
```
PHP Integer
An integer data type is a non-decimal number between -2,147,483,648 and 2,147,483,647.
Rules for integers:
- An integer must have at least one digit
- An integer must not have a decimal point
- An integer can be either positive or negative
- Integers can be specified in: decimal (base 10), hexadecimal (base 16), octal (base 8), or binary (base 2) notation
In the following example $x is an integer. The PHP var_dump() function returns the data type and value:
```
              
    $x = 5985;
    var_dump($x);
              
            
```
PHP Float
A float (floating point number) is a number with a decimal point or a number in exponential form.
PHP Boolean
A Boolean represents two possible states: true or false.

PHP array
An array stores multiple values in one single variable.

              
    $cars = array("Volvo","BMW","Toyota");
    var_dump($cars);

PHP NULL Value
Null is a special data type which can have only one value: NULL.
A variable of data type NULL is a variable that has no value assigned to it.
If a variable is created without a value, it is automatically assigned a value of NULL.
```
              
    $x = "Hello world!";
    $x = null;
    var_dump($x);
              
            
```

PHP Integers

2, 256, -256, 10358, -179567 are all integers.
An integer data type is a non-decimal number between -2147483648 and 2147483647 in 32 bit systems, and between -9223372036854775808 and 9223372036854775807 in 64 bit systems. A value greater (or lower) than this, will be stored as float, because it exceeds the limit of an integer.
Here are some rules for integers:
- An integer must have at least one digit
- An integer must NOT have a decimal point
- An integer can be either positive or negative
- Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based - prefixed with 0x) or octal (8-based - prefixed with 0)
PHP has the following predefined constants for integers:
- PHP_INT_MAX - The largest integer supported
- PHP_INT_MIN - The smallest integer supported
- PHP_INT_SIZE - The size of an integer in bytes
PHP has the following functions to check if the type of a variable is integer:
is_int()

Example :

              
    $x = 5985;
    var_dump(is_int($x));
    $x = 59.85;
    var_dump(is_int($x));

PHP Floats

A float is a number with a decimal point or a number in exponential form.
2.0, 256.4, 10.358, 7.64E+5, 5.56E-5 are all floats.
The float data type can commonly store a value up to 1.7976931348623E+308 (platform dependent), and have a maximum precision of 14 digits.
PHP has the following predefined constants for floats (from PHP 7.2):
- PHP_FLOAT_MAX - The largest representable floating point number
- PHP_FLOAT_MIN - The smallest representable positive floating point number
- -PHP_FLOAT_MAX - The smallest representable negative floating point number
- PHP_FLOAT_DIG - The number of decimal digits that can be rounded into a float and back without precision loss
- PHP_FLOAT_EPSILON - The smallest representable positive number x, so that x + 1.0 != 1.0
PHP has the following functions to check if the type of a variable is float:
is_float()

Example :

              
    $x = 10.365;
    var_dump(is_float($x));

PHP Infinity

A numeric value that is larger than PHP_FLOAT_MAX is considered infinite.
PHP has the following functions to check if a numeric value is finite or infinite:
- is_finite()
- is_infinite()

Example:

              
    $x = 1.9e411;
    var_dump($x);

PHP NaN

NaN stands for Not a Number.
PHP has the following functions to check if a value is not a number:
is_nan()

Example:

              
  $x = acos(8);
  var_dump($x);

PHP Numerical Strings

The PHP is_numeric() function can be used to find whether a variable is numeric. The function returns true if the variable is a number or a numeric string, false otherwise.

Example:

              
  $x = 5985;
  var_dump(is_numeric($x));
  $x = "5985";
  var_dump(is_numeric($x));
  $x = "59.85" + 100;
  var_dump(is_numeric($x));
  $x = "Hello";
  var_dump(is_numeric($x));

PHP Casting Strings and Floats to Integers

Sometimes you need to cast a numerical value into another data type.
The (int), (integer), or intval() function are often used to convert a value to an integer.

              
  // Cast float to int
  $x = 23465.768;
  $int_cast = (int)$x;
  echo $int_cast;
  // Cast string to int
  $x = "23465.768";
  $int_cast = (int)$x;
  echo $int_cast;

PHP Math

PHP has a set of math functions that allows you to perform mathematical tasks on numbers.

Function	Description	Example
pi()	The pi() function returns the value of PI	`echo(pi()); // returns 3.1415926535898`
min() and max()	The min() and max() functions can be used to find the lowest or highest value in a list of arguments	`echo(min(0, 150, 30, 20, -8, -200)); // returns -200 echo(max(0, 150, 30, 20, -8, -200)); // returns 150`
abs()	The abs() function returns the absolute (positive) value of a number	`echo(abs(-6.7)); // returns 6.7`
sqrt()	The sqrt() function returns the square root of a number	`echo(sqrt(64)); // returns 8`
round()	The round() function rounds a floating-point number to its nearest integer	`echo(round(0.60)); // returns 1 echo(round(0.49)); // returns 0`
rand() rand(min,max)	The rand() function generates a random number:	`echo(rand());`
sin() & cos() & tan()	Returns the sine and cosine and tan of a number value in radians
pow()	Returns x raised to the power of y
rad2deg()	Converts a radian value to a degree value

PHP Operators

Arithmetic Operators

operator	Description	EX
(+)	Addition	`$x + $y`
(-)	Subtraction	`$x - $y`
(*)	Multiplication	`$x * $y`
(**)	Exponentiation	`$x ** $y`
(/)	Division	`$x / $y`
(%)	Modulus (Remainder)	`$x % $y`

Assignment Operators

operator	Expression	Same As	EX
(=)	x = y	x = y	`$x = 10`
(+=)	x += y	x = x + y	`$x += 5;`
(-=)	x -= y	x = x - y	`$x -= 5;`
(*=)	x *= y	x = x * y	`$x *= 5;`
(/=)	x /= y	x = x / y	`$x /= 5;`
(%=)	x %= y	x = x % y	`$x %= 5;`

Comparison Operators

Comparison operators are used in logical statements to determine equality or difference between variables or values.

Operator	Description	Comparing	Returns
(==)	equal to	`$x == 8`	false
		`$x == 5`	true
		`$x == "5"`	true
(===)	equal value and equal type	`$x === 5`	true
(===)	equal value and equal type	`$x === "5"`	false
(!=)	not equal	`$x != 8`	true
(!=)	not equal	`$x <> 8`	true
(!==)	not equal value or not equal type	`$x !== 5`	false
		`$x !== "5"`	true
		`$x !== 8`	true
(>)	greater than	`$x > 8`	false
(<)	less than	`$x < 8`	true
(>=)	greater than or equal to	`$x >= 8`	false
(<=)	less than or equal to	`$x <= 8`	true

Increment / Decrement Operators

The PHP increment operators are used to increment a variable's value.
The PHP decrement operators are used to decrement a variable's value.

Operator	Name	Description
++$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

Logical Operators

Logical operators are used to determine the logic between variables or values.

Operator	Description	Example
&&	and	($x < 10 && $y > 1) is true
and	and	($x < 10 and $y > 1) is true
\|\|	or	($x == 5 \|\| $y == 5) is false
or	or	($x == 5 or $y == 5) is false
!	not	!(x == y) is true
xor	xor	$x xor $y

String Operators

the . operator used to add string "concatenate"

EX:

$txt1 = "Hello"; $txt2 = " world!"; echo $txt1 . $txt2;