Arrays & functions in php

Functions In PHP
 Functions are at the heart of a well-organized script and
will make your code easy to read and reuse.
 Large projects would be unmanageable without functions
because the problem of repetitive code would bog down
the development process.
 If you haven’t had much experience using functions, you
can think of a function as an input/output machine. The
machine takes the raw materials you feed it (the input)
and works with them to produce a product (the output).
 A function accepts values, processes them, and then
performs an action (printing to the browser, for example),
returns a new value, or both.

Functions In PHP
 If you need to bake a cake, you would probably do it
yourself, in your own kitchen with your oven. But if you
need to bake thousands of cakes, you would probably
build or acquire a special cake-baking machine, built for
making cakes in massive quantities.
 Similarly, when deciding whether to create a function for
reuse or simply writing in-line code, the most important
factor to consider is the extent to which it can save you
from writing repetitive code.
 If the code you are writing will be used more than once, it
is probably best to create a function to represent the code.

Functions In PHP
 A function is a self-contained block of code that can be
called by your script.
 When called (or invoked), the function’s code is executed
and performs a particular task. You can pass values to a
function (called arguments), which then uses the values
appropriately – storing them, transforming them,
displaying them, whatever the function is designed to do.
When finished, a function can also pass a value back to
the original code that called it into action.
 In PHP, functions come in two flavors – those built in to
the language, and those that you define yourself.

Functions In PHP
 PHP has hundreds of built-in functions. Consider the example shown on
the next page that utilizes the built-in function strtoupper().
 The output from this script is shown below:

Functions In PHP
 In the previous example, the function strtoupper() is
called and passed a variable whose value is represented by a
string. The function goes about its business of changing
the contents of the string to uppercase letters.
 A function call consists of the function name followed by
parentheses. (Note, even a function that has no parameters
requires a set of parentheses.) The information being
passed to the function (the arguments) are placed between
the parentheses.
 For functions that require more than one argument, the
arguments are separated by commas:
some_function ($an_argument, $another_argument);

Functions In PHP
 The strtoupper()from the previous example is typical
for a function in that it returns a value. Most functions
return some information back after they’ve completed their
task – they usually at least tell whether their mission was
successful.
 The strtoupper() function returns a string value so its
usage requires the presence of a variable to accept the
returned string, as was the case in the line:
$capitalized_string – strtoupper($original_string);
 Functions in PHP that return values use a return
statement within the body of the function. We’ll use this in
a few more pages when we start constructing our own
functions.

Defining Functions In PHP
 You can define your own functions in PHP using the
function statement:
function someFunction($argument1,. . .,argument2) {
//function code goes here
}
 The name of the function follows the function statement
and precedes a set of parentheses. If your function requires
arguments, you must place the comma-separated variable
names within the parentheses. These variables will be
filled by the values passed to your function when it is
called.
 Even if your function does not require arguments you must
still supply the parentheses.

 Naming conventions for functions are the same as for
normal variables in PHP. As with variables you should apply
meaningful names and be consistent in naming and style.
Using mixed case in function names is a common
convention, thus myFunction() instead of
myfunction() or my_function(). (Note: variables
names are case sensitive in PHP, function names are not!)
 Let’s define a simple function that simply prints out the word
“Hello” in big letters.
function bigHello() {
echo “<h1> HELLO </h1>”
}

Function
definition
Function call
Function result

Defining Functions With Argument
 For the next example, let’s define a function that requires an
argument. Actually, let’s define two different functions that
each take an argument.
 The first function will take a string and print the string with
a <br /> element appended to the string. The second
function will do the same, but append two <br />
elements to the end of the string.

 For the next example, let’s define a function that requires two
arguments. We’ll basically repeat the exercise from the
previous example, but in this case rather than writing two
different functions that differ only in the number of <br />
elements they append to a line of text, the new function will
have a second argument that represents the number of <br />
elements to be appended. Clearly this would be more efficient,
in terms of code, than creating a different function for each
number of <br /> elements we might want to append.
 In the first version of this example, shown on the next page, I
simply repeated the same effect as in the previous version, so
the two screen shots from the browser should look identical.
 The second version of this example, shown on page 15, a
different effect is produced by the function calls.
Defining Functions With Two Arguments

Passing By Value To Functions
 When you pass arguments to functions, they are stored as
copies in parameter variables. This means that any changes
made to these variables by the function is local to the
function and are not reflected beyond it.
 The example on the next page illustrates argument passing by
value.

Upon return the
value of
$original_num is
unchanged by the
function.

Passing By Reference To Functions
 By default in PHP, variables passed to functions are passed by
value. In other words, only local copies of the variables are
used by the functions and the original values of the variables
are not accessible by the function.
 So how can you allow a function to actually modify a variable
sent to it? You must create a reference to the variable.
 The reference operator in PHP is the & (ampersand). Placing
an ampersand in front of an argument in a function definition
creates a reference to the variable and allows the function to
modify the original variable.
 The following example modifies the previous example to
make use of passing an argument by reference.

The argument $num is passed by
reference since it is preceded with
the & operator.
Upon return from the function the
value of $original_num has
been changed.

Arrays In PHP
 Most of our PHP examples to this point have involved
scalar variables (we did see a couple of example in the first
section of notes that made use of one of PHP’s global
associative arrays).
 Scalar variables can only hold a single value at a time. For
example, a variable $color could hold only a single
value such as red, at any point in time. The variable could
not be used to hold more than one color.
 Arrays are special types of variables that enable you to
store as many values as you want.
Note: Although you can technically make an array as large as you’d like, some built-in
array handling functions in PHP have an upper limit of 100,000 values. If you are storing
more data that this in your arrays and you need to use one of these functions, you will
either need to write your own function or split the data into multiple arrays.

Arrays In PHP
 Arrays are indexed, which means that each entry in the
array, called an element, is made up of a key and a value.
 The key is the index position, beginning with 0 and
increasing incrementally by 1 with each new element in
the array.
 The value is whatever value you associate with that
position – a string, an integer, or whatever you want.
 In PHP you can think of an array as a filing cabinet and
each key/value pair as a file folder. The key is the label
written on the tab of the folder, and the value is what is
inside. What’s inside each folder can vary from folder to
folder.

Creating Arrays In PHP
 You can create an array using either the array()
function or the array operator [].
 The array() function is usually used when you want to
create a new array and populate it with more than one
element, all at the same time.
 The array operator is more often used when you want to
create a new array with just one element at the outset or
when you want to add to an existing array element.
 The examples on the following couple of pages illustrate
creating an array in PHP using these two techniques.

This version uses the
array() function to
create the array.

This version uses the array
operator [ ] to create the array.
Note that no index values are
specified, PHP will auto number for
you

This version also uses the array
operator [ ] to create the array.
Note that index values are specified
in this case.

Creating Arrays In PHP
 As shown in the example on page 44, PHP can
automatically index the array for you when you use the [ ]
operator to create the array.
 This is useful in that it eliminates the possibility that you
might misnumber the elements. The example on the next
page illustrates what happens if you misnumber the
elements in an array.

Misnumbering starts
here with no element 4
defined and then 6 too
is missed.

Creating Associative Arrays In PHP
 The arrays we’ve seen so far have been numerically
indexed, meaning that they use an integer index position
as the key.
 Associative arrays utilize actual named keys. In PHP, the
named keys of an associative array are character strings
rather than numerical values. The string value is used to
look up or provide a cross-reference to the data value.

Iterating through an Array
 A common iterative statement used with both sequential
and associative arrays is the foreach statement.
 The general syntax of the foreach statement is:
foreach ( arrayname as variable ) {
. . . Statements to repeat
}
 The first variable inside the parentheses is the variable name
representing the array and the second variable is
automatically set to the next array item at each iteration of
the loop. An example using a sequential array is shown on
the next page and one with an associative array on the
following page.

Examples of Some Array Functions

Arrays &amp; functions in php

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