Recent Posts
Showing posts with label Blog. Show all posts
Showing posts with label Blog. Show all posts
Sunday, January 1, 2012
String variables are used for values that contain characters.
In this chapter we are going to look at the most common functions and operators used to manipulate strings in PHP.
After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
Below, the PHP script assigns the text "Hello World" to a string variable called $txt:
<?php $txt="Hello World"; echo $txt; ?> |
The output of the code above will be:
Hello World |
Now, lets try to use some different functions and operators to manipulate the string.
The Concatenation Operator
There is only one string operator in PHP.
The concatenation operator (.) is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:
<?php $txt1="Hello World!"; $txt2="What a nice day!"; echo $txt1 . " " . $txt2; ?> |
The output of the code above will be:
Hello World! What a nice day! |
If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string (a space character), to separate the two strings.
The strlen() function is used to return the length of a string.
Let's find the length of a string:
<?php echo strlen("Hello world!"); ?> |
The output of the code above will be:
12 |
The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string).
The strpos() function
The strpos() function is used to search for a character/text within a string.
If a match is found, this function will return the character position of the first match. If no match is found, it will return FALSE.
Let's see if we can find the string "world" in our string:
<?php echo strpos("Hello world!","world"); ?> |
The output of the code above will be:
6 |
The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.
String Variables in PHP
This section lists the different operators used in PHP.
Arithmetic Operators
Operator | Description | Example | Result |
+ | Addition | x=2 x+2 | 4 |
- | Subtraction | x=2 5-x | 3 |
* | Multiplication | x=4 x*5 | 20 |
/ | Division | 15/5 5/2 | 3 2.5 |
% | Modulus (division remainder) | 5%2 10%8 10%2 | 1 2 0 |
++ | Increment | x=5 x++ | x=6 |
-- | Decrement | x=5 x-- | x=4 |
Assignment Operators
Operator | Example | Is The Same As |
= | x=y | x=y |
+= | x+=y | x=x+y |
-= | x-=y | x=x-y |
*= | x*=y | x=x*y |
/= | x/=y | x=x/y |
.= | x.=y | x=x.y |
%= | x%=y | x=x%y |
Comparison Operators
Operator | Description | Example |
== | is equal to | 5==8 returns false |
!= | is not equal | 5!=8 returns true |
<> | is not equal | 5<>8 returns true |
> | is greater than | 5>8 returns false |
< | is less than | 5<8 returns true |
>= | is greater than or equal to | 5>=8 returns false |
<= | is less than or equal to | 5<=8 returns true |
Logical Operators
Operator | Description | Example |
&& | and | x=6 y=3 (x < 10 && y > 1) returns true |
|| | or | x=6 y=3 (x==5 || y==5) returns false |
! | not | x=6 y=3 !(x==y) returns true |
PHP Operators
You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:
- if statement - use this statement to execute some code only if a specified condition is true
- if...else statement - use this statement to execute some code if a condition is true and another code if the condition is false
- if...elseif....else statement - use this statement to select one of several blocks of code to be executed
- switch statement - use this statement to select one of many blocks of code to be executed
The if Statement
Use the if statement to execute some code only if a specified condition is true.
Syntax
if (condition) code to be executed if condition is true; |
The following example will output "Have a nice weekend!" if the current day is Friday:
$d=date("D"); if ($d=="Fri") echo "Have a nice weekend!"; ?> |
Notice that there is no ..else.. in this syntax. The code is executed only if the specified condition is true.
The if...else Statement
Use the if....else statement to execute some code if a condition is true and another code if a condition is false.
Syntax
if (condition) code to be executed if condition is true; else code to be executed if condition is false; |
Example
The following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output "Have a nice day!":
$d=date("D"); if ($d=="Fri") echo "Have a nice weekend!"; else echo "Have a nice day!"; ?> |
If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:
$d=date("D"); if ($d=="Fri") { echo "Hello! "; echo "Have a nice weekend!"; echo "See you on Monday!"; } ?> |
The if...elseif....else Statement
Use the if....elseif...else statement to select one of several blocks of code to be executed.
Syntax
if (condition) code to be executed if condition is true; elseif (condition) code to be executed if condition is true; else code to be executed if condition is false; |
Example
The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise it will output "Have a nice day!":
$d=date("D"); if ($d=="Fri") echo "Have a nice weekend!"; elseif ($d=="Sun") echo "Have a nice Sunday!"; else echo "Have a nice day!"; ?> |
Conditional Statements
Use the switch statement to select one of many blocks of code to be executed.
Syntax
switch (n) { case label1: code to be executed if n=label1; break; case label2: code to be executed if n=label2; break; default: code to be executed if n is different from both label1 and label2; } |
This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.
Example
switch ($x) { case 1: echo "Number 1"; break; case 2: echo "Number 2"; break; case 3: echo "Number 3"; break; default: echo "No number between 1 and 3"; } ?> |
The PHP Switch Statement
A variable is a storage area holding a number or text. The problem is, a variable will hold only one value.
An array is a special variable, which can store multiple values in one single variable.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:
$cars1="Saab"; $cars2="Volvo"; $cars3="BMW"; |
However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The best solution here is to use an array!
An array can hold all your variable values under a single name. And you can access the values by referring to the array name.
Each element in the array has its own index so that it can be easily accessed.
In PHP, there are three kind of arrays:
- Numeric array - An array with a numeric index
- Associative array - An array where each ID key is associated with a value
- Multidimensional array - An array containing one or more arrays
Numeric Arrays
A numeric array stores each array element with a numeric index.
There are two methods to create a numeric array.
1. In the following example the index are automatically assigned (the index starts at 0):
$cars=array("Saab","Volvo","BMW","Toyota"); |
2. In the following example we assign the index manually:
$cars[0]="Saab"; $cars[1]="Volvo"; $cars[2]="BMW"; $cars[3]="Toyota"; |
Example
In the following example you access the variable values by referring to the array name and index:
$cars[0]="Saab"; $cars[1]="Volvo"; $cars[2]="BMW"; $cars[3]="Toyota"; echo $cars[0] . " and " . $cars[1] . " are Swedish cars."; ?> |
The code above will output:
Saab and Volvo are Swedish cars. |
Associative Arrays
An associative array, each ID key is associated with a value.
When storing data about specific named values, a numerical array is not always the best way to do it.
With associative arrays we can use the values as keys and assign values to them.
Example 1
In this example we use an array to assign ages to the different persons:
$ages = array("Peter"=>32, "Quagmire"=>30, "Joe"=>34); |
Example 2
This example is the same as example 1, but shows a different way of creating the array:
$ages['Peter'] = "32"; $ages['Quagmire'] = "30"; $ages['Joe'] = "34"; |
The ID keys can be used in a script:
$ages['Peter'] = "32"; $ages['Quagmire'] = "30"; $ages['Joe'] = "34"; echo "Peter is " . $ages['Peter'] . " years old."; ?> |
The code above will output:
Peter is 32 years old. |
Multidimensional Arrays
In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.
Example
In this example we create a multidimensional array, with automatically assigned ID keys:
$families = array ( "Griffin"=>array ( "Peter", "Lois", "Megan" ), "Quagmire"=>array ( "Glenn" ), "Brown"=>array ( "Cleveland", "Loretta", "Junior" ) ); |
The array above would look like this if written to the output:
Array ( [Griffin] => Array ( [0] => Peter [1] => Lois [2] => Megan ) [Quagmire] => Array ( [0] => Glenn ) [Brown] => Array ( [0] => Cleveland [1] => Loretta [2] => Junior ) ) |
Example 2
Lets try displaying a single value from the array above:
echo "Is " . $families['Griffin'][2] . " a part of the Griffin family?"; |
The code above will output:
Is Megan a part of the Griffin family? |
What is an Array?
Call Me..!!
