Last time we looked at text and strings in variables, in this episode we're going to continue with our exploration of PHP variables and delve deeper into math and number handling in PHP.
Using numbers is not much different to using text and strings, you allocate variables and fill them in, using exactly the same techniques as you do using strings & text.
Basic Operators
The standard arithmetic operators are available in PHP and these are the same as in any other language:
When setting up or assigning variables, you can set the initial value to the result of a mathematical equation, as in the following example:
	$result = 2+2; // $result will be equal to 4
For subtraction and addition there's also a very handy shortcut or two which are great for loop handling, these shortcuts are used by appending either a double + or a double - after the variable name:
The second operator can also be specified as '=num' :
Why would you want to use the shorthand form? Well it turns out that using this method is great for loops and repetitive commands (we'll cover this more in a later article) such as the for loop:
		// Repeat what ever goes here 10 times
In that small example, we start at 0, and keep adding one to $count as long as we are still less than 10.
An IMPORTANT note here, is that a lot of counting structures in PHP start at 0, so in the previous example we are counting from 0 to 9, which is 10 times round before it stops. If we'd changed it to <11 in the middle part, we would have actually performed 11 counts.
Number Shifting
PHP also has a useful operator known as a barrel shifter. The barrel shifter or Logical shift as some people may call it is represented by the << and >> (Chevron) operators.
When applied to a given number, the number is shifted one bit position in that direction. If the idea of shifting seems a little alien then it helps to think of this in terms of binary, and if binary is a little strange, then lets have a little recap first.
Binary what on earth is that?
Human beings are taught at school to deal with the decimal system, in doing this we are taught that numbers start at 0 and go towards 9, once 9 is reached we move across to the next column and continue counting.
The columns are labelled as Hundreds, Tens and Units. Binary numbers are not much different, except that they only go from 0 to 1 before moving across a column.
This for a computer is an absolutely perfect state of affairs, as deep down at the very basic level in a computer, all there is to represent numbers are a series of on or off electrical pulses. Unfortunately this is not so easy for humans to understand, so in order to make it easy to understand we label across the columns in powers of 2 as follows.
	 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
As you can see above, there are 8 columns. When a number is referred to as an 8 bit number, then it is meant that there are 8 columns across the top, a 16 bit number would continue on from 128 to 256, then 512, 1024 and so on multiplying by 2 each time.
If we then put a binary number under the columns, EG:
	 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
	 |  0  |  0 |  1 |  0 | 0 | 1 | 0 | 1 |
You can see where the '1' values lie under the columns, if we add the columns together from right to left, which in this case is 1 + 4 + 32 or 37 so 00100101 = 37 in decimal. To convert back the other way, we simply keep subtracting the largest value we are able to from right to left while still keeping a positive whole number, so
So now we've had a quick recap on binary (I'm not going into it any deeper as this is not a lesson on using binary) why is the barrel shifter so important?
Back to the barrel shifter
As you can see from the above examples, each column in a binary number is a multiplication of 2. The barrel shift, shifts binary bits in a number left and right and as a result is able to multiply and divide by 2 extremely fast. This is very handy if for example we are working with binary streams (such as if we where doing heavy number crunching in a compression system), and if we are chopping up and packing numbers.
Again, if this is a subject that interests you then there are many white papers and educational texts available that cover number theory, just be aware that if your divisions and/or multiplications are powers of two, or if you need to isolate only a single bit in a number then using the barrel shifter is an extremely efficient way to do it.
Number comparisons
In any computer language, the ability to check numbers that are in a given range is a must. You saw it earlier in the example of a for loop, and like loops in general we'll cover decisions in more detail when we cover loops and decisions in a later article, for now though we check ranges by using the following operators:
Normally you would use these in an "if" statement similar to the following:
	if($a > $b)
		// Do stuff if a is greater than b
		// Do stuff if it's not
In this episode we've looked at basic math operations in PHP, and had a recap on binary. As with strings and text there is a huge number of functions that operate on numbers.
There are functions to generate random numbers, or do complex math using sines & cosines.
As always I encourage you to look at the appropriate sections in the PHP Manual, and experiment with what you find there. Remember half of the fun of programming is breaking things, then learning how to fix them.
Until next time Shawty
The ABC's of PHP
Introduction to PHP
What do I need to make it work?
Basic Script Building in PHP
How Variable Am I?
Strings & Text
Math & Number Handling in PHP
Introduction to Arrays and Hashes in PHP
Loops and Decisions in PHP
Advanced String Processing - How Regular Are Your Expressions