Hall of Famer's PHP Tutorials: Chapter 1 - PHP syntax

[Hall of Famer]

Chapter I - PHP Syntax

Well this is the first part of my PHP tutorials, which is all about basic syntax of PHP. In this thread you will be able to learn basic PHP syntax, variables, data types and constants. Alright, lets get this started.


1. Getting started with PHP:
If you have basic knowledge, you should understand the concept of tags. PHP tags enclose lines of PHP codes, you cannot write your PHP codes outside of tags. The start and end tags for PHP is shown below:

PHP Code:

<?PHP
// your codes here
?>

Short tags and complete scripting language tags can be used to replace this basic PHP tags at times:

PHP Code:

<?
// your codes here
?>

PHP Code:

<script language = "php">
// your codes here
</script> 


2. Basic Syntax:
To display a message on the screen, we can use the functions print or echo. Strictly speaking, these are not the type of functions we normally refer to, since there is no need to enclose anything inside parenthesis(). An example is shown below:

PHP Code:

print "hello world";
echo "What a beautiful day!"; 


You may wonder what the semicolon signs are at the end of each line, they represent the end of a PHP statement and must not be left out in PHP programming. Finishing your lines without semicolons will cause severe syntax error, something you apparently do not wish to ever run into.

At times it is rather necessary to write comments so that your codes make sense to you even if you have taken a long break from PHP programming. It will also help other programmers read your script files. To write comments, simply use double slashes in front of your sentences:

PHP Code:

// This is a comment 


Now that we have understood the basis of PHP syntax, lets move on to variables, something you will have to use a lot in any programming languages.


3. Variables:
A variable is a type of container, which holds one particular value that can be of any data type. You can only assign one value to a variable, and the value can be changed at any time. To create a PHP variable, use the syntax:

PHP Code:

$var = value; 


Here the dollar sign "$" indicates that you are working with a variable, 'var' is the name of our variable. The 'value' is whatever you assign to this variable, it can be a strong, an integer, a double floating number and so on. The equal sign "=" is technically not an equal sign, it assigns a value to the variable you define. Examples of Variables definition are shown below:

PHP Code:

$num = 10;
$name = "Sarah";
$pi = 3.14159265; 


Do not ever forget the semicolon at the end of each line, or you will receive a fatal error. An interesting fact about PHP is that it automatically recognizes data types such as int, string or double. This saves you significant amount of work when defining a variable.

Another very important thing about variables is that its name can only contain letters, numbers or underscores. A variable name beginning with a number is not valid, nor is a variable that contains spaces. Examples of valid variable names are shown below:

PHP Code:

$name
$w75t
$_t013yuf 


The following variables names are, however, invalid in PHP:

PHP Code:

$8543pod
$re+arb
$my food 


4. Data Types:
Data types are not that important in PHP compared to C++ and Ruby, but it is still important to play around with them. There are six basic data types, namely:

integer: 8, 99, 100000
double: 1.5, 2.6666, 3.14
boolean: true and false
string: "Anna", "Hello World".
array
object
null
resource

It may be necessary to see what data type a variable is currently holding. To do this, use the function below:

PHP Code:

gettype($var) 


The data type of variable $var will be printed to the screen if 'echo' is added right in front of the function gettype(). Another useful function is to set datatype to a different one:

PHP Code:

settype($var, datatype) 


This function takes in two arguments, the variable name and the newly assigned datatype. This way you can convert a variable from integer to double or string easily. A good example is shown below:

PHP Code:

$num = 3.1415926;
settype($num, int);
echo $num; 


The result is integer 3 on your screen, isnt this amazing? Datatype conversion is usually done by PHP itself, but there are times that you will have to do this yourself.

You may also use PHP's built-in functions is_datatype($var) to test if a variable contains the desired datatype. This types of functions return true if the variable contains the same datatype, or it returns false. They can be easily integrated with if...else statements.

A list of this type of functions is shown below:

PHP Code:

is_int($var)
is_double($var)
is_string($var)
is_bool($var)
is_array($var
is_object($var)
is_null($var)
is_resource($var) 


5. Constants:
Constants, in contrast to variables, are containers storing values that cannot be changed later in your codes. To create a PHP constant, use the following syntax below:

PHP Code:

define("Constant's name", value); 


Keep in mind that once a constant has been defined, its value will no longer subject to reassignment. An example of constant definition is shown below:

PHP Code:

define("NAME", "Richard");
echo NAME; 


The screen shall display the name Richard. Note it is common practice to define your constants with all upper-case letters, or the script may confuse a constant with a string.


Alright, this is all for basic syntax. The next tutorial will introduce the concept of operators and how they work in PHP. This is my first time writing tutorials for PHP programming, lemme know if you have any suggestions on this. Thanks for reading this thread everyone, and have fun with Mysidia Adoptables script files. ^^