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Now, after we learned how to show content and also had a first glance at variables, we will now go a step further.
To define a variable in PHP you just need to use $ and a variable name: $variable.
You can use as variable name whatever you like, however you are not allowed to let it start with a number, like $1variable and there are also some predefined variables, about which I will talk later.
There are many types of variables, but for now we concentrate on 4 types (actually 5, but the fifth will follow in another tutorial).
So, which 4 types do we have?
string
e.g. $string = "This is a string";
boolean
e.g. $boolean = True;
integer
e.g. $integer = 123456;
float
e.g. $float = 1.234;
so, let’s make a script where can play a bit with those variables:
<?PHP
$string= "This is a string"; // String
$string_alt= 123456; // String
$boolean= True; // Boolean
$integer= 123456; // Integer
$float= 1.234; // Float
print 'The variable "$string" has the type of: '.gettype($string).'<br />';
print 'The variable "$string_alt" has the type of: '.gettype($string_alt).'<br />';
print 'The variable "$boolean" has the type of: '.gettype($boolean).'<br />';
print 'The variable "$integer" has the type of: '.gettype($integer).'<br />';
print 'The variable "$float" has the type of: '.gettype($float);
?>
Run this script and the gettype() function will tell you which type a variable has.
If you have a look at the output, you will see a mistake. Isn’t „$string_alt“ supposed to have the type „string“?
Yes, it is supposed to be a string, however, PHP does not know that your number shall be a string. So how can fix this problem?
It is quite easy, just add (string) infront of it, so it looks like $string_alt= (string) 123456; // String.
Everything should be fine now, you could even turn the string back to integer, just add (integer) again:
<?PHP
$string_alt= (string) 123456; // String
print 'The variable "$string_alt" has the type of: '.gettype($string_alt).'<br />';
$string_alt = (integer )$string_alt; // convert to Integer
print 'The variable "$string_alt" has the type of: '.gettype($string_alt);
?>
What we did here is called „type casting“ and it is always useful if you have script where you need to change the variable type to prepare it for a special function or whatever you plan to do with it. You can find a complete list of the type casting in the PHP documentation at the official website.
Type casting is not the only thing you can do variables. You can also add $variable1 at the end (or beginning) of $variable2:
<?PHP
$start = "The little brown fox ";
$end = "jumped over the green fence.";
$start_merge = $start;
$start_merge .= $end; // adds behind the existing content
print 'Start sentence: '.$start.'<br />';
print 'End sentence: '.$end.'<br /><br />';
print 'Correct sentence: '.$start_merge.'<br />';
print 'Correct sentence: '.$start.$end.'<br />';
?>
As you will see our sentence will be shown in different ways. So let us have a closer look at the code itself:
The „.=“ means, that the variable which shall be added to another one will be added at the end of the other variable
The „$start.$end“ looks, familiar, doesn’t it? I mentioned it in PHP Tutorial 101: Hello World! and the same behavior you see there also happens here.
Before I go on with some mathematical things we can do, I will tell you about the „//“ I added to the code because I assume you are wondering what it means Image may be NSFW.
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The double-slashes only exclude a comment of the code. Beside the „//“ you can also use „/* comment */“ and „#“
The „//“ comment will end either at the end of the line of code where it is placed; Everything on the same line and behind of the slashes belong to the comment.
The „/* comment */“ starts at „/*“ and ends at „*/“ no matter if there are multiple lines of code or not.
The „#“ comment behaves like the „//“ comment.
So, as we have this explained, I’m able to use more comments in the code and avoid longer „outside of code“ explanations Image may be NSFW.
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Now let’s do some mathematics!
With PHP (as with any other programming language) you are able to make all kind mathematic calculations. For this tutorial, I only stick to the most basic mathematic functions and refer you to the PHP Manual: Mathematical Functions
We will use the following script as a start for some calculations:
<?PHP
$a = 5;
$b = 2.3;
$c = -6;
$d = 100;
$ad = $a + $d; // Adds $d to $a
$da = $a - $d; // Subtracts $d from $a
$bc = $b / $c; // Divides $b through $c
$dc = $d * $c; // Multiplies $b with $c
print $a.' + '.$d.' = '.$ad.'<br />';
print $a.' - '.$d.' = '.$da.'<br />';
print $b.' / '.$c.' = '.$bc.'<br />';
print $d.' x '.$c.' = '.$dc.'<br />';
?>
We just did the basic mathematic calculations you and I think it is self-explanatory, so let’s have a look how we can get a random number, divide it by another random number and make sure the result is rounded to 2 decimal places, if it is a floating number:
<?PHP
$random_a = rand(1,1000); // get a random number between 1 and 1000
$random_b = rand(500,1500); // get a random number between 500 and 1500
$random = $random_a / $random_b;
$random_round = round($random,2); // rounds result to 2 decimal places
print 'First random number is: '.$random_a.'<br />
Second random number is: '.$random_b.'<br />
Result is: '.$random.'<br />
Rounded result is: '.$random_round;
?>
Of course there are way more things you can do, but I think this is enough for mathematics. I recommend you have a look at the PHP Manual: Mathematical Functions and play around because it is proved that you learn much more by the „Trial and Error“ concept that any other Tutorial.
A tutorial is always a start, but you really learn something by doing it on your own. So use the time to the next tutorial by training what you have learned. Image may be NSFW.
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Update: Here you see a page with the results of the code used in this tutorial