Welcome to PHP. This tutorial is aimed at beginner PHP developers who want to learn how to use the PHP's in-built logical operators.

Let’s say you have two savings jars, one for notes and one for coins. A friend gives you some money. If it’s a note, you want put it in the notes jar, otherwise it must be a coin and goes with the coins. How do you code this in PHP? Well, we simply use an operator called IF!

Before we get any further, lets discuss the logic of operators. To start off you call the operator. Next you define the arguments. Then you define the instructions that will be carried out when the arguments are correct. If you have more than one instruction to be processed in the event of the argument(s) being correct, you enclose them in curly brackets. i.e. { /*instructions*/ }.

If...Else Statements
Ok, let’s start with the IF operator. We will use our example above and code it. The logic is the same - i.e. if the money is a note, add it to the note box:

And it’s done. As you only have one instruction, you don’t need curly brackets. This script will check whether the variable $money is equal to the text “note”, and if so, adds a “ ” and the value of $money to the $notes variable.   is XHTML for a line drop, so when you output the variable you can see the individual entries.

.= is syntax that you can use instead of = [] + []. i.e. instead of typing $var = $var . $iable you can simply replace it with $var .= $iable. Other similar syntax formats you can use are: +=, -=, %=, *= and /=.

But what happens when $money is not equal to “note”?. To handle this, we use the ELSE operator:

The human translation of this code is quite simple: "if $money is equal to “note” then add the value of $money to the $notes variable, otherwise add it to the $coins variable".

To finish up our section on the IF statement, let’s look at how to define multiple conditions. We can use either && (and) or || (or) or simply the word “AND” or “OR”:

Of course, if you execute the above code, you will get the value of money appearing twice, because both statements are the same. That said, let’s move on to looping.

Looping
There are 3 main ways to use loop structures. The basic structure is: while [argument] is true, process instructions then re-iterate.

The first example I will outline uses WHILE, and is possibly the easiest looping structure. Let’s make a simple number generator that will output the numbers from 1 to 50 inclusive on a new line. Pleas note that <= means 'less than or equal to', >= means 'greater than or equal to', == means 'equal to', and != means 'not equal to'.

$i++ is a simple instruction, adding 1 to variable $i. You can also use $i += 1 or $i = $i + 1, if that is your way - it’s just preference really!

Simple enough? Good. Let’s move on to FOR statements. The FOR statement simply incorporates definition of the identifier, the argument and the last instruction into one line. The logic is: for [define identifier], [condition], [what to do with identifier] instructions. Let’s rewrite the above code with the FOR statement instead:

<?php

for($i = 1; $i <= 50; $i++) echo $i . " ";

?>

Note that I didn’t use curly brackets simply because there is only 1 instruction now. You can use them if you like, but it will not affect the output.

Let’s say you wanted to do this script in reverse order, i.e. output 50 to 1 inclusive. We simply define $i as 50, change the matching operator to greater than or equal to 1, and use $i-- instead of $i++.

<?php

for ($i = 50; $i >= 1; $i--) echo $i . " ";

?>

The last loop structure I will look at is FOREACH. This structure is only used for arrays, to iterate over each value in the array. The logic for this structure is: FOREACH [array] is [variable]. So, let’s use it to build an array first, then output each value, and produce what we did in the previous examples:

<?php

$numbers = array();

for($i = 1; $i <= 50; $i++) $numbers[$i] = $i;

foreach($numbers as $currentnum) echo $currentnum . " ";

?>

Done! That wasn’t too hard was it? $numbers is the name of the array, and $currentnum contains the current array data. This script does exactly the same as the two examples for WHILE and FOR, except it uses an array to hold the numbers. This example wouldn’t be as practical as the others as it would probably be slower, but FOREACH is good for array handling.

The last topic I will cover in this tutorial is SWITCH structure.

Switches
Switches work basically the same as a whole bunch of IF/ELSEIF/ELSE statements. Using SWITCH(), you define a case for each possibility, and if you need/want to, a default case that handles all other values. Going back to our first example with the money jars, let’s write a switch using those guidelines, including an error handling “default” case. Default cases must go last.

<?php

switch($money){

case "note":
$notes .= " " . $money;
break;

case "coin":
$coins .= " " . $money;
break;

default:
echo "What kind of money is this? It’s not note or coin form!";
break;

}

?>

This code says what the others say, but if $money isn’t a coin or note, is outputs an error message! Cool, huh?

I don’t like it when people use many ELSEIF’s to represent complex choices, so I encourage people to use SWITCH instead. This is why I haven’t included any ELSEIF explanations in my tutorial.

Anyway, best of luck with PHP! If you are interested and want to learn more advanced features of PHP, there are plenty of tutorials here at BioRUST that will help you in most areas of PHP, many that I have written personally. There are a couple of advanced tutorials covering GDlib, Cryptography and mcryptlib too, so don't be shy!

You can contact me for help via the Creative Forums, or click my name below to visit my profile, where you can email or PM me. Have fun!


	Introduction to PHP: Logical Operators Tutorial Author - Scrowler (http://forums.biorust.com/member.php?userid=66)