PHP Tutorial for Beginners - Part 5
Arrays
An Array is a sort of multi-valued variable. It stores one or more values, each one identified by a number representing its position in the array. The exact syntax is shown below
We're referring to the sixth element of the array named myArray. Sixth because array elements always begin with 0. Thus if we use [10], we would be referring to the 11th element of the array.
Similarly to assign the value 5 to the second element of the same array we could use the following
PHP Code:
$myArray[1] = 5;
In case you want to have the third value of the array named $myArray stored in a variable named $myVariable we could use
PHP Code:
$myVariable = $myArray[2];
Arrays are often used to hold values of related variables. For example there are 100 students and all their ages have to be stored in a program. Instead of using 100 Integer variables, we would use one array (aptly named $ages[100]) which is an array of 100 Integers. This way it would lead to neater and better design on the program. You could then access the 100 elements of such an array using $ages[0] .... $ages[99] .
Array Declaration Methods
The declaration of an array variable can be made by listing the elements that the array would hold right at the time when you declare the array.
PHP Code:
$varArray = array (element1, element2, ..., elementN);
$varArray is the name we chose for the array variable, while element1, element2 ... elementN are the values stored in the array in position 1, 2... N.
There is a second way to declare an array variable. It is possible to assign a value to each position of the array through the following syntax
PHP Code:
$varArray[0] = element1;
$varArray [1] = element2;
.
.
.
$varArray [N-1] = elementN;
Both the above methods perform the same assignment. The first one is more compact, but you need to know the values that you would enter in the array right at the time when you initialize the array. Whereas the second method involves assigning each element of the array one at a time. So you could (if required) compute a particular value in the middle of your program and then assign it any particular array element.
Note : Remember that the first element of an Array is always identified by number zero (0). This means that if an array holds eight elements, they will be numbered from Array[0] to Array[7].
Adding elements to an array
Adding elements to an array (append instruction) can be possible in PHP using the following syntax
PHP Code:
$varArray[] = newvalue;
This instruction would append the value ' newvalue ' to a new element after the existing last element in the array. Suppose the array had 5 values (arrayname[0] ..... arrayname[4]) and you had the above statement, the new value would be assigned to 6th element of that array (arrayname[5]).
Example of using Arrays
Using an Array data type could be useful during data processing operations, too. If we decide to save variables in one array object it would be easier to manage them. This because it is possible to process (read/write/edit) all of them by using a loop structure (for loop or while loop). In fact the loop's control variable would be used as the array's index.
Now we are going to define an array and print its content with a for loop. Then we'll add a new value to the array and finally we'll print the array again. This is the code for the program
PHP Code:
<HTML>
<BODY>
<?
$vv = array ("<BR>","Welcome to ", "Bit After Bit. ", "Loading, just ", 5, " minutes");
for ($k=0;$k<6;$k++)
echo ($vv[$k]);
$vv[]= " or a little more!";
for ($k=0;$k<7;$k++)
echo ("$vv[$k]");
?>
</BODY>
</HTML>
The script above would generate an HTML page which displays the following
Quote:
Welcome to Bit After Bit. Loading, just 5 minutes
Welcome to Bit After Bit. Loading, just 5 minutes or a little more!
Scalar and Associative Arrays
The array variables we've discussed till now are all scalar arrays. Working with scalar arrays, you can access to any elements through an index.
PHP allows to define a second kind of arrays called the associative arrays. An associative array is an array in which the elements can be accessed through a keyword instead of the index. Each element, in an associative array, is characterized by a keyword. This means we'll no more use indexes to read/write/edit elements, because they have been replaced by keywords. The associative arrays is constituted by pairs such as "key - element".
The syntax we'll use to define an associative array is similar to that we have used to define scalar array. We just need to replace indexes with keywords.
PHP Code:
$varArray = array (
"key1" => element1;
"key2" => element2;
...
"keyN" => elementN;
);
varArray is the name of the array variable , key1, key2..., keyN are the N keywords through which we can access the respective elements - element1, element2, ... elementN.
Look at the following example where associative arrays are used
PHP Code:
$website = array(
"name" => "Bit After Bit",
"URL" => "http://www.bitafterbit.com",
"email" => "[email protected]",
);
An associative array with three elements has been defined. The first element, accessible through the keyword "name" is of string type and contains the value "Bit After Bit". The second element is a string too, it is accessible through keyword "URL" and stores the value "http://www.bitafterbit.com". The third and last element is also a string containing the value "[email protected]".
Once we have defined such an array we could use the following script to display some of the values
Sample Program
PHP Code:
<?
echo ("Surf to the website $website[name] at $website[URL]!");
?>
Output of above program
That's it!! We have covered all the necessary basics that any beginner would like to learn. I hope you'll have enjoyed this series as much as I have enjoyed writing it..
