PHP Tutorial – Part 4 – How to Use Loops and Arrays In PHP

Introduction

In the last parts of this tutorial I have showed you how to deal with text and variables in PHP and how you can use IF statements to compare them and to make decisions. In this part I am going to show you how to use another important part of PHP, loops.

The WHILE Loop

The WHILE loop is one of the most useful commands in PHP. It is also quite easy to set up and use. A WHILE loop will, as the name suggests, execute a piece of code until a certain condition is met.

Repeating A Set Number Of Times

If you have a piece of code which you want to repeat several times without retyping it, you can use a while loop. For instance if you wanted to print out the words “Hello World” 5 times you could use the following code:

$times = 5;
$x = 0;
while ($x < $times) {
echo "Hello World";
++$x;
}

I will now explain this code. The first two lines are just setting the variables. The $times variable holds the number of times you want to repeat the code. The $x variable is the one which will count the number of times the code has been executed. After these is the WHILE line. This tells the computer to repeat the code while $i is less than $times (or to repeat it until $i is equal to $times). This is followed by the code to be executed which is enclosed in { }.

After the echo line which prints out the text, there is another very important line:

++$x;

What this does is exactly the same as writing:

$x = $x + 1;

It adds one to the value of $x. This code is then repeated (as $x now equals 1). It continues being repeated until $x equals 5 (the value of times) when the computer will then move on to the next part of the code.

Using $x

The variable counting the number of repeats ($x in the above example) can be used for much more than just counting. For example if you wanted to create a web page with all the numbers from 1 to 1000 on it, you could either type out every single one or you could use the following code:

$number = 1000;
$current = 0;
while ($current < $number) {
++$current;
echo "$current
“;
}

There are a few things to notice about this code. Firstly, you will notice that I have placed the ++$current; before the echo statement. This is because, if I didn’t do this it would start printing numbers from 0, which is not what we want. The ++$current; line can be placed anywhere in your WHILE loop, it does not matter. It can, of course, add, subtract, multiply, divide or do anthing else to the number as well.

The other reason for this is that, if the ++$current; line was after the echo line, the loop would also stop when the number showed 999 because it would check $current which would equal 1000 (set in the last loop) and would stop, even though 1000 had not yet been printed.

Arrays

Arrays are common to many programing languages. They are special variables which can hold more than one value, each stored in its own numbered ‘space’ in the array. Arrays are extremely useful, especially when using WHILE loops.

Setting Up An Array

Setting up an array is slightly different to setting up a normal variable. In this example I will set up an array with 5 names in it:

$names[0] = ‘John’;
$names[1] = ‘Paul’;
$names[2] = ‘Steven’;
$names[3] = ‘George’;
$names[4] = ‘David’;

As you can see, the parts of an array are all numbered, starting from 0. To add a value to an array you must specify the location in the array by putting a number in [ ].

Reading From An Array

Reading from an array is just the same as putting information in. All you have to do is to refer to the array and the number of the piece of data in the array. So if I wanted to print out the third name I could use the code:

n
echo “The third name is $names[2]“;

Which would output:

The third name is Steven

Using Arrays And Loops

One of the best uses of a loop is to output the information in an array. For instance if I wanted to print out the following list of names:

Name 1 is John
Name 2 is Paul
Name 3 is Steven
Name 4 is George
Name 5 is David

I could use the following code:

$number = 5;
$x = 0;
while ($x < $number) {
$namenumber = $x + 1;
echo "Name $namenumber is $names[$x]
“;
++$x;
}

As you can see, I can use the variable $x from my loop to print out the names in the array. You may have noticed I am also using the variable $namenumber which is always 1 greater than $x. This is because the array numbering starts from 0, so to number the names correctly in the output I must add one to the actual value.

PHP Tutorial – Part 3 – How to Use IF- Else Statements in PHP

Introduction

Over the past two parts I have shown you the basics of text in PHP and how to store it as variables. In this part of the tutorial I will show you how to use IF statements to make decisions in your scripts.

The Basics Of IF

If statements are used to compare two values and carry out different actions based on the results of the test. If statements take the form IF, THEN, ELSE. Basically the IF part checks for a condition. If it is true, the then statement is executed. If not, the else statement is executed.

IF Strucure

The structure of an IF statement is as follows:

IF (something == something else)
{
THEN Statement
} else {
ELSE Statement
}

Variables

The most common use of an IF statement is to compare a variable to another piece of text, a number, or another variable. For example:

if ($username == “webmaster”)

which would compare the contents of the variable to the text string. The THEN section of code will only be executed if the variable is exactly the same as the contents of the quotation marks so if the variable contained ‘Webmaster’ or ‘WEBMASTER’ it will be false.

Constructing The THEN Statment

To add to your script, you can now add a THEN statement:

if ($username == “webmaster”) {
echo “Please enter your password below”;
}

This will only display this text if the username is webmaster. If not, nothing will be displayed. You can actually leave an IF statement like this, as there is no actual requirement to have an ELSE part. This is especially useful if you are using multiple IF statements.

Constructing The ELSE Statement

Adding The ELSE statement is as easy as the THEN statement. Just add some extra code:

if ($username == “webmaster”) {
echo “Please enter your password below”;
} else {
echo “We are sorry but you are not a recognised user”;
}

Of course, you are not limited to just one line of code. You can add any PHP commands in between the curly brackets. You can even include other IF statments (nested statements).

Other Comparisons

There are other ways you can use your IF statement to compare values. Firstly, you can compare two different variables to see if their values match e.g.

if ($enteredpass == $password)

You can also use the standard comparision symbols to check to see if one variable is greater than or less than another:

if ($age $finished)

You can also check for multiple tests in one IF statement. For instance, if you have a form and you want to check if any of the fields were left blank you could use:

if ($name == “” || $email == “” || $password == “”) {
echo “Please fill in all the fields”;
}

PHP Tutorial Part 2 – Displaying Information & Variables

Introduction

In the last part of the tutorial I explained some of the advantages of PHP as a scripting language and showed you how to test your server for PHP. In this part I will show you the basics of showing information in the browser and how you can use variables to hold information.

Printing Text

To output text in your PHP script is actually very simple. As with most other things in PHP, you can do it in a variety of different ways. The main one you will be using, though, is print. Print will allow you to output text, variables or a combination of the two so that they display on the screen.

The print statement is used in the following way:

print(“Hello world!”);

I will explain the above line:

print is the command and tells the script what to do. This is followed by the information to be printed, which is contained in the brackets. Because you are outputting text, the text is also enclosed instide quotation marks. Finally, as with nearly every line in a PHP script, it must end in a semicolon. You would, of course, have to enclose this in your standard PHP tags, making the following code:

Which will display:

Hello world!

on the screen.

Variables

As with other programming languages, PHP allows you to define variables. In PHP there are several variable types, but the most common is called a String. It can hold text and numbers. All strings begin with a $ sign. To assign some text to a string you would use the following code:

$welcome_text = “Hello and welcome to my website.”;

This is quite a simple line to understand, everything inside the quotation marks will be assigned to the string. You must remember a few rules about strings though:

Strings are case sensetive so $Welcome_Text is not the same as $welcome_text
String names can contain letters, numbers and underscores but cannot begin with a number or underscore
When assigning numbers to strings you do not need to include the quotes so:

$user_id = 987

would be allowed.

Outputting Variables

To display a variable on the screen uses exactly the same code as to display text but in a slightly different form. The following code would display your welcome text:

As you can see, the only major difference is that you do not need the quotation marks if you are printing a variable.

Formatting Your Text

Unfortunately, the output from your PHP programs is quite boring. Everything is just output in the browser’s default font. It is very easy, though, to format your text using HTML. This is because, as PHP is a server side language, the code is executed before the page is sent to the browser. This means that only the resulting information from the script is sent, so in the example above the browser would just be sent the text:

Hello and welcome to my website.

This means, though, that you can include standard HTML markup in your scripts and strings. The only problem with this is that many HTML tags require the ” sign. You may notice that this will clash with the quotation marks used to print your text. This means that you must tell the script which quotes should be used (the ones at the beginning and end of the output) and which ones should be ignored (the ones in the HTML code).

For this example I will change the text to the Arial font in red. The normal code for this would be:

As you can see this code contains 4 quotation marks so would confuse the script. Because of this you must add a backslash before each quotation mark to make the PHP script ignore it. The code would chang
e to:

You can now include this in your print statement:

print(“Hello and welcome to my website.“);

which will make the browser display:

Hello and welcome to my website.

because it has only been sent the code:

Hello and welcome to my website.

This does make it quite difficult to output HTML code into the browser but later in this tutorial I will show you another way of doing this which can make it a bit easier.

Learn PHP yourself by this tutorial – Introduction to PHP

Introduction

Up until recently, scripting on the internet was something which very few people even attempted, let alone mastered. Recently though, more and more people have been building their own websites and scripting languages have become more important. Because of this, scripting languages are becomming easier to learn and PHP is one of the easiest and most powerful yet.

What Is PHP?

PHP stands for Hypertext Preprocessor and is a server-side language. This means that the script is run on your web server, not on the user’s browser, so you do not need to worry about compatibility issues. PHP is relatively new (compared to languages such as Perl (CGI) and Java) but is quickly becomming one of the most popular scripting languages on the internet.

Why PHP?

You may be wondering why you should choose PHP over other languages such as Perl or even why you should learn a scripting language at all. I will deal with learning scripting languages first. Learning a scripting language, or even understanding one, can open up huge new possibilities for your website. Although you can download pre-made scripts from sites like Hotscripts, these will often contain advertising for the author or will not do exactly what you want. With an understanding of a scripting language you can easily edit these scripts to do what you want, or even create your own scripts.

Using scripts on your website allows you to add many new ‘interactive’ features like feedback forms, guestbooks, message boards, counters and even more advanced features like portal systems, content management, advertising managers etc. With these sort of things on your website you will find that it gives a more professional image. As well as this, anyone wanting to work in the site development industry will find that it is much easier to get a job if they know a scripting language.

What Do I Need?

As mentioned earlier, PHP is a server-side scripting language. This means that, although your users will not need to install new software, you web host will need to have PHP set up on their server. It should be listed as part of your package but if you don’t know if it is installed you can find out using the first script in this tutorial. If you server does not support PHP you can ask your web host to install it for you as it is free to download and install. If you need a low cost web host which supports PHP I would recommmend HostRocket.

Writing PHP

Writing PHP on your computer is actually very simple. You don’t need any specail software, except for a text editor (like Notepad in Windows). Run this and you are ready to write your first PHP script.

Declaring PHP

PHP scripts are always enclosed in between two PHP tags. This tells your server to parse the information between them as PHP. The three different forms are as follows:

PHP Code In Here

All of these work in exactly the same way but in this tutorial I will be using the first option (). There is no particular reason for this, though, and you can use either of the options. You must remember, though, to start and end your code with the same tag (you can’t start with <? and end with for example).

Your First Script

The first PHP script you will be writing is very basic. All it will do is print out all the information about PHP on your server. Type the following code into your text editor:

As you can see this actually just one line of code. It is a standard PHP function called phpinfo which will tell the server to print out a standard table of information giving you information on the setup of the server.

One other thing you should notice in this example is th
at the line ends in a semicolon. This is very important. As with many other scripting and programming languages nearly all lines are ended with a semicolon and if you miss it out you will get an error.

Finishing and Testing Your Script

Now you have finished your script save it as phpinfo.php and upload it to your server in the normal way. Now, using your browser, go the the URL of the script. If it has worked (and if PHP is installed on your server) you should get a huge page full of the information about PHP on your server.

If your script doesn’t work and a blank page displays, you have either mistyped your code or your server does not support this function (although I have not yet found a server that does not). If, instead of a page being displayed, you are prompted to download the file, PHP is not installed on your server and you should either serach for a new web host or ask your current host to install PHP.

It is a good idea to keep this script for future reference.

Part 2

In this part I have introduced you to the basics of writing and running PHP. By this time you should now know if your host supports PHP and should have a basic understanding of how PHP scripts are structured. In part 2 I will show you how to print out information to the browser.

Object-Oriented Programming Concepts

If you’ve never used an object-oriented programming language before, you’ll need to learn a few basic concepts before you can begin writing any code. This lesson will introduce you to objects, classes, inheritance, interfaces, and packages. Each discussion focuses on how these concepts relate to the real world, while simultaneously providing an introduction to the syntax of the Java programming language.

What Is an Object?

An object is a software bundle of related state and behavior. Software objects are often used to model the real-world objects that you find in everyday life. This lesson explains how state and behavior are represented within an object, introduces the concept of data encapsulation, and explains the benefits of designing your software in this manner.

What Is a Class?

A class is a blueprint or prototype from which objects are created. This section defines a class that models the state and behavior of a real-world object. It intentionally focuses on the basics, showing how even a simple class can cleanly model state and behavior.

What Is Inheritance?

Inheritance provides a powerful and natural mechanism for organizing and structuring your software. This section explains how classes inherit state and behavior from their superclasses, and explains how to derive one class from another using the simple syntax provided by the Java programming language.

What Is an Interface?

An interface is a contract between a class and the outside world. When a class implements an interface, it promises to provide the behavior published by that interface. This section defines a simple interface and explains the necessary changes for any class that implements it.

What Is a Package?

A package is a namespace for organizing classes and interfaces in a logical manner. Placing your code into packages makes large software projects easier to manage. This section explains why this is useful, and introduces you to the Application Programming Interface (API) provided by the Java platform.

What Is an Object?

Objects are key to understanding object-oriented technology. Look around right now and you’ll find many examples of real-world objects: your dog, your desk, your television set, your bicycle.
Real-world objects share two characteristics: They all have state and behavior. Dogs have state (name, color, breed, hungry) and behavior (barking, fetching, wagging tail). Bicycles also have state (current gear, current pedal cadence, current speed) and behavior (changing gear, changing pedal cadence, applying brakes). Identifying the state and behavior for real-world objects is a great way to begin thinking in terms of object-oriented programming.

Take a minute right now to observe the real-world objects that are in your immediate area. For each object that you see, ask yourself two questions: “What possible states can this object be in?” and “What possible behavior can this object perform?”. Make sure to write down your observations. As you do, you’ll notice that real-world objects vary in complexity; your desktop lamp may have only two possible states (on and off) and two possible behaviors (turn on, turn off), but your desktop radio might have additional states (on, off, current volume, current station) and behavior (turn on, turn off, increase volume, decrease volume, seek, scan, and tune). You may also notice that some objects, in turn, will also contain other objects. These real-world observations all translate into the world of object-oriented programming.

A software object.

Software objects are conceptually similar to real-world objects: they too consist of state and related behavior. An object stores its state in fields (variables in some programming languages) and exposes its behavior through methods (functions in some programming languages). Methods operate on an object’s internal state and serve as the primary mechanism for object-to-object communication. Hiding internal state and requiring all interaction to be performed through an object’s methods is known as data encapsulation — a fundamental principle of object-oriented programming.
Consider a bicycle, for example:

A bicycle modeled as a software object.
By attributing state (current speed, current pedal cadence, and current gear) and providing methods for changing that state, the object remains in control of how the outside world is allowed to use it. For example, if the bicycle only has 6 gears, a method to change gears could reject any value that is less than 1 or greater than 6.
Bundling code into individual software objects provides a number of benefits, including:
1. Modularity: The source code for an object can be written and maintained independently of the source code for other objects. Once created, an object can be easily passed around inside the system.
2. Information-hiding: By interacting only with an object’s methods, the details of its internal implementation remain hidden from the outside world.
3. Code re-use: If an object already exists (perhaps written by another software developer), you can use that object in your program. This allows specialists to implement/test/debug complex, task-specific objects, which you can then trust to run in your own code.
4. Pluggability and debugging ease: If a particular object turns out to be problematic, you can simply remove it from your application and plug in a different object as its replacement. This is analogous to fixing mechanical problems in the real world. If a bolt breaks, you replace it, not the entire machine.

Objective-C

Object-oriented programming, like most interesting new developments, builds on some old ideas, extends them, and puts them together in novel ways. The result is many-faceted and a clear step forward for the art of programming. An object-oriented approach makes programs more intuitive to design, faster to develop, more amenable to modifications, and easier to understand. It leads not only to new ways of constructing programs, but also to new ways of conceiving the programming task.
Nevertheless, object-oriented programming presents some formidable obstacles to those who would like to understand what it’s all about or begin trying it out. It introduces a new way of doing things that may seem strange at first, and it comes with an extensive terminology that can take some getting used to. The terminology will help in the end, but it’s not always easy to learn. Moreover, there are as yet few full-fledged object-oriented development environments available to try out. It can be difficult to get started.
That’s where this book comes in. It’s designed to help you become familiar with object-oriented programming and get over the hurdle its terminology presents. It spells out some of the implications of object-oriented design and tries to give you a flavor of what writing an object-oriented program is really like. It fully documents the Objective-C(tm) language, an object-oriented programming language based on standard C, and introduces the most extensive object-oriented development environment currently available–OPENSTEP(tm).
The book is intended for readers who might be interested in:
• Learning about object-oriented programming,
• Finding out about the OPENSTEP development environment, or
• Programming in Objective-C.
NeXT supplies its own compiler for the Objective-C language (a modification of the GNU C compiler) and a run-time system to carry out the dynamic functions of the language. It has tested and made steady improvements to both over the years; this book describes the latest release, which includes provisions for declaring and adopting protocols and setting the scope of instance variables.
Throughout this manual and in other NeXT documentation, the term “Objective-C” refers to the language as implemented for the OPENSTEP development environment and presented here.
________________________________________
The Development Environment
________________________________________
Every object-oriented development environment worthy of the name consists of at least three parts:
• A library of objects and software frameworks and kits
• A set of development tools
• An object-oriented programming language
OPENSTEP comes with an extensive library. It includes several software frameworks containing definitions for objects that you can use “off the shelf” or adapt to your program’s needs. These include the Foundation Framework, the Application Kit(tm) framework (for building a graphical user interface), and others.
OPENSTEP also includes some exceptional development tools for putting together applications. There’s Interface Builder(tm), a program that lets you design an application graphically and assemble its user interface on-screen, and Project Builder, a project-management program that provides graphical access to the compiler, the debugger, documentation, a program editor, and other tools.
This book is about the third component of the development environment–the programming language. All OPENSTEP software frameworks are written in the Objective-C language. To get the benefit of the frameworks, applications must also use Objective-C. You are not restricted entirely to Objective-C, however; you are free to incorporate C++ code into your applications as well.
Objective-C is implemented as set of extensions to the C language. It’s designed to give C a full capability for object-oriented programming, and to do so in a simple and straightforward way. Its additions to C are few and are mostly based on Smalltalk, one of the first object-oriented programming languages.
This book both introduces the object-oriented model that Objective-C is based upon and fully documents the language. It concentrates on the Objective-C extensions to C, not on the C language itself. There are many good books available on C; this manual doesn’t attempt to duplicate them.
Because this isn’t a book about C, it assumes some prior acquaintance with that language. However, it doesn’t have to be an extensive acquaintance. Object-oriented programming in Objective-C is sufficiently different from procedural programming in standard C that you won’t be hampered if you’re not an experienced C programmer.
________________________________________
Why Objective-C
________________________________________
The Objective-C language was chosen for the OPENSTEP development environment for a variety of reasons. First and foremost, it’s an object-oriented language. The kind of functionality that’s packaged in the OPENSTEP software frameworks can only be delivered through object-oriented techniques. This manual will explain how the frameworks work and why this is the case.
Second, because Objective-C is an extension of standard ANSI C, existing C programs can be adapted to use the software frameworks without losing any of the work that went into their original development. Since Objective-C incorporates C, you get all the benefits of C when working within Objective-C. You can choose when to do something in an object-oriented way (define a new class, for example) and when to stick to procedural programming techniques (define a structure and some functions instead of a class).
Moreover, Objective-C is a simple language. Its syntax is small, unambiguous, and easy to learn. Object-oriented programming, with its self-conscious terminology and emphasis on abstract design, often presents a steep learning curve to new recruits. A well-organized language like Objective-C can make becoming a proficient object-oriented programmer that much less difficult. The size of this manual is a testament to the simplicity of Objective-C. It’s not a big book–and Objective-C is fully documented in just two of its chapters.
Objective-C is the most dynamic of the object-oriented languages based on C. The compiler throws very little away, so a great deal of information is preserved for use at run time. Decisions that otherwise might be made at compile time can be postponed until the program is running. This gives Objective-C programs unusual flexibility and power. For example, Objective-C’s dynamism yields two big benefits that are hard to get with other nominally object-oriented languages:
• Objective-C supports an open style of dynamic binding, a style than can accommodate a simple architecture for interactive user interfaces. Messages are not necessarily constrained by either the class of the receiver or the method selector, so a software framework can allow for user choices at run time and permit developers freedom of expression in their design. (Terminology like “dynamic binding,” “message,” “class,” “receiver,” and “selector” will be explained in due course in this manual.)
• Objective-C’s dynamism enables the construction of sophisticated development tools. An interface to the run-time system provides access to information about running applications, so it’s possible to develop tools that monitor, intervene, and reveal the underlying structure and activity of Objective-C applications. Interface Builder could not have been developed with a less dynamic language.

object-oriented programming

Object-oriented programming (OOP) is a programming language model organized around “objects” rather than “actions” and data rather than logic. Historically, a program has been viewed as a logical procedure that takes input data, processes it, and produces output data.
The programming challenge was seen as how to write the logic, not how to define the data. Object-oriented programming takes the view that what we really care about are the objects we want to manipulate rather than the logic required to manipulate them. Examples of objects range from human beings (described by name, address, and so forth) to buildings and floors (whose properties can be described and managed) down to the little widgets on your computer desktop (such as buttons and scroll bars).
The first step in OOP is to identify all the objects you want to manipulate and how they relate to each other, an exercise often known as data modeling. Once you’ve identified an object, you generalize it as a class of objects (think of Plato’s concept of the “ideal” chair that stands for all chairs) and define the kind of data it contains and any logic sequences that can manipulate it. Each distinct logic sequence is known as a method. A real instance of a class is called (no surprise here) an “object” or, in some environments, an “instance of a class.” The object or class instance is what you run in the computer. Its methods provide computer instructions and the class object characteristics provide relevant data. You communicate with objects – and they communicate with each other – with well-defined interfaces called messages.
The concepts and rules used in object-oriented programming provide these important benefits:
• The concept of a data class makes it possible to define subclasses of data objects that share some or all of the main class characteristics. Called inheritance, this property of OOP forces a more thorough data analysis, reduces development time, and ensures more accurate coding.
• Since a class defines only the data it needs to be concerned with, when an instance of that class (an object) is run, the code will not be able to accidentally access other program data. This characteristic of data hiding provides greater system security and avoids unintended data corruption.
• The definition of a class is reuseable not only by the program for which it is initially created but also by other object-oriented programs (and, for this reason, can be more easily distributed for use in networks).
• The concept of data classes allows a programmer to create any new data type that is not already defined in the language itself.
Simula was the first object-oriented programming language. Java, Python, C++, Visual Basic .NET and Ruby are the most popular OOP languages today. The Java programming language is designed especially for use in distributed applications on corporate networks and the Internet. Ruby is used in many Web applications. Curl, Smalltalk, Delphi and Eiffel are also examples of object-oriented programming languages.
OOPSLA is the annual conference for Object-Oriented Programming Systems, Languages and Applications.

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