Write PHP Scripts Part I

PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. Over 20 million websites use PHP today. Sites like eBay, Yahoo, and NASA are using PHP. Most website tasks can be tackled using PHP, and the great thing is it's not hard to learn.

Introduction

PHP is a wildly popular server side scripting language used on over 20 million websites including industry-leaders like eBay, Yahoo!, and NASA. If NASA trusts PHP, then I think it's safe to say PHP is very solid.

PHP scripts are embedded right inside plain HTML documents and are processed on the server computer, sending pure HTML back to the vistors browser. Calling PHP a server-side scripting language means the scripts are read, processed, and output is written from the server computer.
PHP scripting has many benefits for developers over other scripting languages. Unlike JavaScript and VBScript, PHP doesn't require a special browser or plug-ins to run. All browsers can view pages created with PHP. The PHP Engine is also free for anyone to download and install, and can be installed on Windows, Linux, and Macintosh machines.

Who Is This Article Written For

• This article assumes you have no previous programming training.
  
• If you do have previous programming training, then the concepts explained here should come easy. PHP borrows heavily from the C/C++ programming language.

F.A.Q

Q: What does PHP stand for?
A:  PHP is a recursive acronym that stands for PHP Hypertext Preprocessor.

Q:  What do I need to run PHP scripts?
A:  See the section below, Things You'll Need.

Things You'll Need

• The Apache Web Server [ How to install ]
  
• PHP
  
• A Text Editor
  
• A Web Browser

Conventions used in this tutorial

There are a few keywords and images you should watch out for when reading this article.



Things you should know before starting

• This article assumes you've installed Apache and PHP on your computer. Anytime it's said to save a file, you are saving in the htdocs directory inside the Apache directory.
• When saving files in Windows Notepad, wrap the filename in double quotations so that Notepad doesn't at .txt to the end of the filename. That means you would type the filename like this
  
  
  
  Notice the file helloworld.php has " " around it. You have to do this or Notepad will save the file as helloworld.php.txt

Your First Script

Let's jump right into writing your first script, and then I'll explain what's going on.
Open Notepad (Start->All Programs->Accessories->Notepad). You'll be using Notepad a lot.

Type the following into Notepad:

<?php

    echo 'Hello World!'; 

?>

Save this file as "helloworld.php". Open your favorite browser and type this address in the address bar:
http://localhost/helloworld.php

This is what you should see in your browser window

Hello World!


Nothing fancy here, but you did write your first PHP script.



With that in mind,

Type the following into Notepad:

<?php

    echo '<strong>Hello World!</strong>';

?>

Save the file as "helloworld2.php", and open your browser by using the address:
http://localhost/helloworld.php

This time in your browser you'll see

Hello World!


The output is the same as before, but this time the text is in bold.

<strong></strong>

is HTML markup to print all text between the tags as bold.

This demonstrates that any output sent from the PHP engine is treated as HTML by your browser.

Let's write the same script as before, but add another echo statement.

Type the following into Notepad:

<?php

    echo 'Hello World!<br />';

    echo 'How are you doing?'; 

?>

Save this as "helloworlddouble.php". When you run the script in your browser, you should see this

Hello World!
How are you doing?


This prints to your browser window probably what you were expecting. The thing you need to notice is the

<br />

on the first line. This is HTML markup to insert a line break. If you didn't add this, your output would look like this

Hello World!How are you doing?


Now that you've mastered the echo statement, let's move on to something a bit more complicated.

Variables

You can think of variables as containers for data. To manipulate data, be it numbers or names, you need to store the data in a container. The syntax for assigning data, or better called a value, into a variable is

$myVariable = 'Hello World!';

In the above example, the value is 'Hello World!', and the variable is $myVariable. You're telling PHP to store the value at the right of the equals sign, into the variable at the left of the equals sign.


Now let's do something fun with a variable.

Type the following into Notepad:

<?php

    $myVariable = 'Hello World!'; 

    echo $myVariable; 

?>

Save the file as "myfirstvariable.php". When you browse to this script with your browser, the output should look like this

Hello World!



Variables can also contain numbers, and then those numbers can be manipulated using simple mathematical functions. Take this next script for example.

Type the following into Notepad

<?php

    $mySmallNumber = 12;

    $myLargeNumber = 356;

    $myTotal = $mySmallNumber + $myLargeNumber;

    echo $myTotal; 

?>

Run this script in your browser, you should see this

368


Nothing real impressive, but you did add two variables together.


Conclusion

In the first part of this article you have learned to output basic text to your browser, and you have learned about variables. While these things might not seem amazing, many of the things you will do in PHP rely on these basic fundamentals.

In the next part of this tutorial, you will learn about data types and how to further manipulate variables.


Write PHP Scripts Part II

PHP is a powerful scripting language aimed at the web. The language allows you to make any page dynamic as long as you have the proper setup. This tutorial assumes that you have read through Part I.

Things You'll Need

• A working PHP installation (You should have this if you have been through the first half)

Introduction

This tutorial covers datatypes along with the if statement. These will build the foundation to any program you wish to write.

The if statement allows the language to ask questions. This adds flexibility that is necessary for even the most basic projects you could wish to complete. This construct allow the program to conditionally execute behavior.

Data-types

Data-types differentiate one piece of data from another. There are an infinite number of data-types in PHP, because the language allows you to define your own data-types. However, that is beyond the scope of this tutorial. The three data-types that we will be concerned with are strings, numbers and booleans.

Numbers

Of these data-types, numbers are the most fundamental. Numbers are numbers, that’s really about all there is to them. All basic arithmetic operations exist in PHP and numbers react to them exactly as you would expect. It is easy to assign a number value to a variable:

$myVar = 3;

$myVar = 3.0;

Strings

A string represents an indeterminate list of characters. These characters can be anything, Greek letters, numbers, anything that can be represented in a computer. Most data that will be placed on the page will be from string data-types. Strings must be enclosed by either double or single quotes. You declare a string variable like this:

$myStringVar= “hello world”;

$myStringVar2 = ‘hello world’;

Variables can be placed inside strings in what is called inline replacement. This allows you to replace the variable with whatever you would like. For instance:

$name = 'John';

$message = “Hello $name”;

Would render as “Hello John”. This allows you to make messages that vary depending on who is visiting the site.

Booleans

Booleans represent a true or false value. Think of it as a yes or no. Booleans are vital in PHP as answers to questions that your program will ask. PHP will treat anything as a Boolean if you place it in a Boolean context. PHP treats a lot of things as true, while relatively few things are false. The following objects are treated as false:

• The number 0
   
• The number 0.0
   
• The empty string ''
   
• The string '0'

This is by no means a complete list of false values; however, it is everything that is false within the scope of this tutorial.


Branching Construct

Branching constructs are the fundamental decision makers in PHP. When you use a branching construct you are able to specify behavior based on a condition. Using this behavior allows you to check for errors in data, verify that a user has the correct credentials to access a portion of your site, or anyplace else that you want your program to conditionally execute code.

If Statement

The if statement is the workhorse branching construct. Once you understand this, you will find yourself using it in almost every program that you write. An if statement allows the program to ask a yes/no question and then execute a specified behavior depending on the answer. The if statement can be used a few different ways. The first is to execute a behavior if the answer to the question is true and do nothing if it is false:

if($myVar) {

  echo “myVar is true”;

}

In this instance, “myVar is true” would be output to the page only if the value of $myVar were true. (See the Booleans section for questions about what is true in PHP).
This is great, but now you say, “What if I want to do something if my question is false”. That’s easy. You use an else with the if. Here is how:

if($myVar) {

  echo “myVar is true”;

}else {

  echo “myVar is false”;

}

Here we have a behavior for when $myVar is true, and then an else statement for when $myVar is false. If $myVar is true, then it evaluates as it did above. Otherwise, this statement will cause “myVar is false” to be rendered to the page.
There is a third way to use the if statement that allows you to specify more than to behaviors. Its called the else if. You specify one or more conditions and then the behavior to execute if that condition is met. Here is an example:

if($myVar<0){

   echo “myVar is negative”;

}

else if($myVar>0){

   echo “myVar is positive”;

}else{

   echo “myVar is zero”;

}

When used this way, you are able to specify an infinite number of possible outcomes, allowing your program to react to as many different inputs as you want.