PHP
PHP code can be included alone inside a file or can be embedded inside the html code and runs on webserver. The PHP files have extension of .php. The PHP code syntax is:
<?php
‘code goes here’
?>
We have to use semi colon at the end of each command/line.
If we only have php code in a file, then we need to make sure that there is no space before the opening php tags or after the closing php tag.
If the file extension is .php then we can only view that file through web browser where php is installed even if the file does not have any php code.
On our local servers we need to store the files in the root folder, which for WAMP is C:\wamp\www. We also need to make sure that the local server is running. The local port is 80, if we are using a different port than standard then we need to specify that e.g. http://localhost:8888/.
We can have as many blocks of php codes inside html as we want. However, we cant nest one php code inside another.
We can also insert php code above the html code and that works perfectly fine. The php code directly works with the database so if we are not outputting anything in html the code above html code works just fine.
. Period:
Period is used to concatenate two strings.
Variable:
In PHP all variable name start with ‘$’ sign e.g. $name = ‘Ali’;. Remember ‘$this’ is a reserved variable so don’t use this.
Some people use parenthesis around variable but it is completely optional to use.
String:
The php string works the same way as Python. Php stores text only as string.
We can concatenate two strings with ‘.’ Dot or we can also concatenate two or more strings by placing the string variables in double quotes.
There are many string functions which we can use to manipulate strings.
Strtolower(string); – converts the string to lower case
Strtoupper(string); – converts the string to upper case
Ucfirst(string); – converts the first alphabet to upper case.
Strlen(string); – tells us the length of thestring.
Trim(string); – remove whitespaces
Strstr(string_name, “string which we are trying to find”); – first we place the string and second the string which we are looking for. The result returns the word/string we were looking for and everything after that. This is find function.
Str_replace(“string which we want to replace”, “the string which to replace by”, “string which we are looking into”);
Str_repeat(string, number of times we want it to repeat); - this function we first mention the string and then the number of times we want the string to repeat.
Substr(string, position where we want to start displaying the string, position where we want to end displaying the string); - this function displays part of the string, we specify the position from and to. The number starts from 1, not 0.
Strops(string which we want to look in, string which we want to find); - this function will return the position of the string which we want to find within the string.
Strchr(string in which we want to find, chr for which we want to find the position); - this function helps us find the position of a specific character.
And there are more.
Integer/Float Data Type:
‘Is_int’(here we can place a value, it can be variable) is a function which tells us is the value is integer or not by true or false.
‘is_float’(value) behaves that same way as is_int(value) so also is is_numeric(value).
Print/echo:
Print function is like Python print; it simply prints content in browser. PHP also uses echo for this purpose. There is not much difference so I can use either but there is a small difference which I will have to learn when I am at advance level.
Print or echo can also be written as ‘<?=’ this is a short hand of writing echo.
Include:
In php we can use include function. We can basically create php files, which we believe will be common to our site and then instead of writing the same code for each page, where needed we can simply call the include file by placing simple include code. The syntax is:
<?php include ‘folder_name/file_name.php’; ?>
The include file almost works as extension of the page where the include file is being called from. Therefore, we do not need to have any html start and end codes as we normally do, we can simply start by writing the exact common code that we want. The code can include html and php code.
It is common practice to store all include files in a separate one folder for easy maintenance. If the include file is in the same folder then call the file as ‘./file_name.php’.
There are four different type of include commands that can be used. * Include * Include includes file but if the file is not found, the program keeps going. * Require * Require includes file but if the file is not found the script stops. * include once * require once
Include once and require once are normally used during extreme programming for limited purposes. Therefore, include and require are basically two options for the most part.
It is good to use include for the following scenarios. * Functions * Layout sections * Reusable HTML/PHP code * CSS and JavaScript
Page Redirection:
The page redirection is very important concept in php, it is mostly used when we have a user take an action and based on the results we redirect them to different pages e.g. if a user logs in. if the login is successful, the user will be taken to one page and if the user is failed to login, the user is taken to a different page.
We can use 302 redirect. It has two parts: first HTTP 1.1/302 found and another the location: path. header(“Location: new-url”); exit; we need to use exit since this is what tells the page to do the redirect and exist right after. One used case of the redirect is that we can place the above code in a function and then check if a user is logged in or not, if a user is logged in we can call our function and pass page location of one page but if the user is not logged in then we can pass page location of a different page.
The redirect request always need to be at the top of the page. It needs to be the first thing on a page since if it is not the HTTP header request will get passed on and will be too late to change it.
Output buffering:
The concept of output buffering is that in general php is a server side language, we write commands which are passed on to the server for processing. The output buffering give us ability to hold the execution within php, manipulate it before we pass it to the server for processing. This give us more control over our code. We can turn on or off the output buffering. The control to turn it on or off lives in php.ini file. By default it is turned off. We can also start the buffer within the application by writing the following command.
Ob_start() – to start the buffer. Ob_end_flush() – to end the buffer.
Array:
PHP array is equal to Python list. The syntax is:
Array_variable = array(‘values go here’); or
Array_variable = [];
Also, newer versions of php use ‘[‘values go here’]; ‘ format also.
If you want to add additional value to the existing array, it is going to be added at the end of the array. The syntax is:
‘‘variable_name’[] = ‘str_value’;’
If we want to replace one value in array with new value we can specify the position of the value we want to replace. The syntax is:
“variable_name[4]” = ‘str_value’
This type of array is called index array. When we want to print values of array we need to use ‘print_r (array name goes here)’. This function not only list the values of array but also their position so it is excellent tool in examining an array. Php array starts the same way as Python which is from position zero.
The echo or print command in array only works if we also include the position of the array e.g. $flowers[3]. $flowers is a name of array. If we want the complete array to display on screen using echo/print we need to first convert it to string. We do that by using function called ‘implode’.
The syntax is: ‘echo implode(str, array_name);’. The string can be an empty string to add space between values. Without the empty string the array will display but the values will have no spaces between them e.g. ‘echo implode(array_name);’ will have display values but will have no space.
Data submitted from online forms normally is stored in array.
We can create array where we have a key and value. The syntax is: array( ‘key_name’ => ‘string’,
….
)
This type of array is called associative of array. It is used to easily identify elements inside the array. With these array we don’t relay too much on the position rather than use key to pull the value of the array. When order matter, we want to use index array but if it does not and want to call something by a key associative array is a better option.
We can also have multi-dimensional array. These arrays have array within array. The syntax is:
Array(
‘key_name’ => array(‘str’, ‘str’, ‘str’….),
‘key_name’ => array(‘str’, ‘str’….)
);
We can also have array within one array and so forth.
Array Functions:
Some of the array built-in functions are: * Count(‘array name’); * Max(‘array name’); * Min(‘array name’); * Sort(array name); - sorts the array * Rsort(array name); - reverse sort array * Implode(“place how you want the array values to be separated”, array name); - this converts array into string * explode(“place how you want the string values to be separated”, string name); - this converts string into array * in_array(value that we are looking for, array name); - find the value in array and return true or false. * Current(array name) – tells you a position of the value in array, if it is first statement it will tell the position of the first value. * Next(array name) – take the code to the next value in an array. * Prev(array name) – takes the code of the previous value in an array * Reset(array name) – resets the position of the code to the first value in an array * End(array name) – give the position of the last value in an array * There are many array functions on php online documentation
Booleans:
Booleans is either a value true or false.
In php true if represented by ‘1’ and false is represented by ‘ ‘.
Juggling and Type Casting:
Juggling:
Gettype(variable name); - get the data type of the variable
Casting:
Settype(variable name, “name of the datatype in which we want to change the variable to”); - lets you set a datatype of a variable to a specific datatype.
Constants:
Constants are what don’t change for the duration of the php script or you cannot redefine them, they stay to the same value which you define it the first time. But the constant is set for only one run script. When the script is run second time, it can be reassigned but then it will stay constant for that duration of the script run. The syntax is:
Define(“CONSTANT NAME”, value which we want to assign to constants); - the constant name is always in caps.

If:
In php the if statement syntax is:
If (condition goes here){ Script goes here
}
Elseif is written as elseif, rather than elif as Python. And is written as ‘&&’ and Or is written as ‘||’. Not is written as ‘!’.
Equal to is ‘==’. Identical is ‘===’. The difference between identical and equal is that to be identical both side have to be same data type also in addition to equal. For equal to, the data type does not have to be same.
Not identical is ‘!==’. Not equal is ‘!=’. compare is ‘<’, ‘>’, ‘>=’, ‘<=’, ‘<>’.
Switch Statements:
The syntax is:
Switch (value){
Case test_value1: Statement
Case test_value2: Statement
Default:
Statement
}
The difference between if and switch is that the switch does not really look for true/false in Booleans statements like if. It checks test cases and whichever case is true, it execute that case. E.g. we can test to see if a customer contacted us via email, phone or some other mean. Each of these cases are test cases and we will execute different statement for each statement. In most cases we use if statement but there are some case where switch is better suited. Another very major difference between if and switch that in switch when a case is true, it automatically executes all cases subsequent to it. If we don’t want that behavior we can use break; command after each case. The behavior of executing all subsequent cases after a case is true is really handy when we want to execute same set of code in case of two or more cases. In that case we can just simply write them after one another and not have a break. E.g.
Switch (value){
Case test_value1: Statement;
Case test_value2:
Case test_value3:
Case test_value4: Statement;
}
While Loop:
The syntax is:
While (expression) { Statement;
}
The expression is Booleans statement. We basically say is the expression is true, execute the code and it keeps looping until the expression is false.
For Loop:
The syntax is:
For (expr1; expr2; expr3;…) ‘or in other words, it is for (initialize; expr; exist_statement) { Statement;
}
Foreach loop to loop arrays:
In php we can use foreach loop to loop through arrays. The difference between foreach and while, for loop is the foreach loop is used for arrays and stop automatically at the end of array. In for and while loop, we need to specify when the loop need to stop executing. The syntax foreach loop is: foreach (array_name as variable_name){ condition }
This loop works very similarly as for loop in Python, it loops through an array one by one. We can specify html syntax to show how we want the loop to display array values. If we want to use echo while we are loop through an array, the syntax is: echo ‘could by any html tag or empty’ . array_name . ‘could be any html tag or empty’.
. When we are looping through an associative of an array we need to make sure to use curly bracket ‘{}’ around array name is we are using double quotes to display a message. In associative of array we can display only the values of the array or both the key and value of the array when looping through it. When we only want the values to be displayed the syntax is:
Foreach (array_name AS variable_name){ echo “<p>variable_name</p>”;
}
If we want the key and the value the syntax is and it is also used for multi-dimensional array: foreach (‘array_name’ AS ‘key_name_variable’ => ‘value_name_variable’){ Echo “<p> any text we want to display ‘key_name’ and any text if we want ‘value_name</p>”;
}
Continue:
Continue lets you skip a step and allow the code to continue. It is normally used in cases where we don’t need to take any action. E.g. if we say look at student database if they are not signed up send them email but if they are don’t do anything, in that case we can use continue and if a student is signed up continue and don’t do anything. The syntax is: Continue;
When we have nested loops and if condition is true we want to skip the child loops and directly go back up to parent loop, we can code that in the continue such as if we have two one nested loop, we can say continue(2); it will skip back up to the parent loop. By default each continue function has a value of 1 e.g. continue(1); but we normally don’t have to write that.
Break:
Break stops the loop and exists. In programming it is helpful if we are looping over something and want to find something and after we find it, we just want to simply exist since we found what we were looking for.
If we have nested loops, by default if we have a break statement in a child loop, the code will break out of the child loop but will continue parent loop. However, we want to completely break out of the loop we can specify that within break. E.g. break(2) will break out of both loops if there were two loops.
In array:
Php has an in_array function which simply checks if a value is inside an array or not. The syntax is: if (in_array(‘variable_name which has value we are checking’, ‘array_name’){ code goes here;
}
Function:
The syntax is:
Function function_name($arg1, $arg2,…) { Statement;
}
PHP functions work very similar to Python, we can define functions and then call them within our code whenever we want/need to.
To call function we simply call the name of the function with arguments such as function_name(arg1_value, arg2_value,…);. This also works very similar as Python, we can pass on whatever value we want to pass on as arguments when calling function.
Same as Python, when we define functions we specify the arguments and when we are calling the function we define the value which we are passing in those arguments. We can pass in variables the values and it does not matter what we are calling function arguments and variables, what matters is the position and the number of arguments are have. If we have three arguments, we need to pass on three values and which value will be passed on to which argument depends on the position the names don’t have to match.
We can use return function, which works very similarly as Python. We can use the return function and it will return the value from function back to where we are calling the function from. The syntax is:
Return name_of_what_we_want_to_return;
If we only do echo it is going to echo and loss the value, but return store the value back in a variable which we can use for further functioning. Return also works somewhat as break, if used in the middle of the function, as soon as it is meet, it will return the value and break the code. Best practice is to return the value and use it in whatever way you want to use it. If we echo it within our function it is not a good practice.
In general we can only return one value for each function. If we want to return more than one value, we can use array to store those multiple values and then return them. The syntax is:
Return array($first_value_we_want_return, $second_value_we_want_return);
We can store the returned array value in a variable and then use it the same way as we use array values.
We can also specify the arguments value in the within where we are defining function and then we don’t need to pass on a value to the arguments but if we do it will overwrite the default argument value. The syntax is:
Function function_name(“arg1” = “default_value”, “arg2” = “default_value)
To call this: function_name ()
List:
In PHP lists are used to organize the multiple values are get from a function in the form of array, we can assign those values to values in a list, which makes it more organized and easy to use in our code. The syntax is:
List ($variable_name, $variable_name,…) = function_name_which_we_are_calling(value1, value2,..);
Variable Scope:
In PHP we have global and local variables. When we call variables within function, the variables within function are local variables. We cannot call them from outside of the function. If we want to call a function which is define inside from outside we can define it as global. The syntax is:
Global variable_name;
How PHP works:
PHP code is executed when user take an action. There could be URLs/Links which can be passed to the PHP code, forms, or cookies.
In PHP when URLs/Links are passed PHP uses GET method. For Forms PHP uses POST method. And for cookies, PHP uses cookies method.
Post:
The post method is used for forms and form data. In php the post is called super global array, which means array is automatically created when page is submitted. When post function is used and online form is submitted, the form information is automatically stored in post array. The post array creates associative array so the key is the name of the field and the appropriate value is called using array key, which is the field name.
We can initiate post function from any input field. E.g. lets say if the form submit button is called ‘Submit’, the syntax will be following:
<?php
if (isset($_POST[‘Submit’])){ code goes here
}
?> isset is another function used to check if submit has been submitted or not.
HTML post function takes the values submitted through the form in the html headers and pass it to database. If there is no html action function is called, the form simply reloads after submitting the data.
Detecting Form:
When we use post method, fill out the form, and hit submit, which takes us to next page where the data is stored in the form of an array. It works fine but if we directly want to load the page where the data is stored, we get an error. That is because the array keys come back and basically complain that there is no data to be stored. We have a couple of options to use to not have this issue.
We can use if statement and basically ask if the username is set or not and same thing for any other value we are trying to get. The syntax is:
If (isset($_POST[“array_key”])){ Code;
}
A better way to check if the form was submitted or not we can check if form was submitted. That will take care of the error. The benefit is that before we do any kind of processing, we can check if the form was submitted or not. If the form was submitted we can do more processing, if not we can just stop. The syntax is:
If (isset($_POST[‘name_of_submit_button’]){
CODE;
}
Ternary Operator:
With the above code the issue is it will be long code if we have to write that for every possible option on our form. There is another way to write the same code which is by ternary operator. This is actually another way of writing if statement. The syntax is:
Boolean_test ? value_if_true : value_if_false
So basically we say: first test the condition, the second portion after question mark state execute me if test is true otherwise execute else statement which is after second question mark.
Get:
HTML get function adds field name and values to the end of the url. The syntax is: $_GET
The php get method automatically creates associative array. It is also super global array. The get method is mostly used for getting the information from a search key when someone tries to put in search information that they want to search for. However, it could also be used to get information from any other form. The key to remember is that the get function gets the data from name and value from the url, which is added towards the end of the url.
Get is http method that relates to the URLs passed by.
In theory, we can pass any value in the urls but there are some reserved characters in PHP which has special meaning. The reserved characters are as follow and we have to convert them in their hexadecimal form by using ‘%’ sign with 2 digit hexadecimal.
! - %21, # - %23, $ - %24, & - %26, ‘ - %27, ( - %28, ) - %29, * - %2A, + - %2B, , - %2C, / - %2F, : - %3A, ; - %3B, = - %3D, ? - %3F, @ - %40, [ - %5B, ] - %5D
We convert them in the hexadecimal form by using function called urlencode($string_name);.
The urlencode function takes letters, numbers, underscore, and dashes as is, which is unchanged. It takes that reserved characters and convert them in % with 2 digit hexadecimal. And spaces become ‘+’.
Without urlencode, if we try to get the url and if any of the reserved words are being used, it will not get the entire url properly. The urlencode is only used for the urls.
PHP has another function rawurlencode, which works very similar as urlencode with the difference that rawurlencode takes spaces and convert them into ‘%20’ as compared to ‘+’ sign as urlencode does.
The urls have in general two components, the first portion is before ‘?’ sign and that contains the path to the files on the server. The portion contained after ‘?’ sign is a query string. In general rawurlencode is more compatible with browsers therefore if we have doubt which method is support we should use rawurlencode for both portions of the url to cover spaces. However, rawurlcode needs to be used for the portion of the url before ‘?’. For portion after ‘?’ the spaces should be encoded by urlencode since ‘+’ is more efficient way to encode query strings.
File systems only understand ‘%20’. If we use ‘+’, the browser will not find file on the file server.
Reserved Characters in HTML:
There are some characters in html that has special meaning e.g. opening tag ‘<’ and closing tag ‘>’. These reserved characters if used will cause the html to behave differently than how we want it to be. Therefore, we need to use special functions every time we use these reserved characters to make sure that the html reads them and converts them properly. There are the following reserved characters in html. We need to encode them to make sure they do not case issue. We can encode html using two different functions. When we encode them, it outputs to the users in the form that user understands.
‘<’ - &lt;, ‘>’ - &gt;, ‘&’ - &amp;, ‘”’ - &quot;,
The first function we can use in php to encode html special characters is htmlspecialchars($string_name);. The second function is htmlentities($string_name). the htmlentities covers a lot more use cases than htmlspecialchars and used normally when we are using large block of text, htmlspecialchars only cover the 4 characters listed above.
Type juggling during comparisons:
It following the following basic rules when doing comparisons: * String vs. null: converts null to “ “ * Boolean vs. other: converts other to Boolean * Number vs. other: converts other to number
If we are doing comparison and want to make sure php does not do type juggling, we need to make sure we use ‘===’.
Empty:
In php we have the following items which we consider empty.
“ “, 0, “0”, null, false, array()
Cookies:
The cookies are stored in web browsers and read by php code. We store user status in browser cookies to know that multiple requests are coming from same user. Without that we would not know. The process starts when a user submits request to a server. The server send back the status which it wants to store in user browser and that is sent under header, by set-cookie command. At that point the browser store the cookie in local computer and from that point all the requests that the user sends to the server it also sends the browser cookie which was initially stored. That how the server know it is the same user who sent initial request again sending other requests and treats it accordingly. The cookies are send in the header and the cookies cannot be set manually, it is only set when a request is sent.
PHP takes the cookie value and stores it in a super global array and the syntax is: $_COOKIE;. It is another associative array.
Set Cookie Value:
The php function to set cookie is: setcookie($name, $value, $expire);
The name is the name we want to give to our cookie. The value is what we assign to the cookie and expire is after how long we want the cookie to expire. We don’t store the cookies forever so we set it to expire in 24hours, week, year, etc.
Setting cookies come before any html code unless output buffering is on. The users can see what values we stored in cookies so we need to be sure we don’t store anything confidential or that will give opportunity to hack into our site.
Get Cookie Value:
We can get the users cookies information by function called $_COOKIE[“name_of_cookie”];. We can store it in a variable and learn some behavior of the user such as what language preference the user has.
Unsetting Cookie Values:
We need to be able to unset cookie values as well. When a user logs in. we store the user id in cookie, after they logout we want to be able to remove the user id. To unset cookie, we can use setcookie function and set it to null or we can also set a time for expiration. The best case is to use both of these options combined. The syntax is: * Setcookie($name, null); * Setcookie($name, $value, (time() – 3600));
Sessions:
The sessions are related to cookies but they are stored on the web server instead of the web browser as we do it with cookies. The main difference between the two is that with sessions we can store lot more information than we can with cookie. When we store information in session on the web server, we send a reference to the user browser, from that point every time user sends a request, the request also contains the reference number and we are able to pull the information from the session. * The cookie is limit to 4000 character but on the session it is limit to the hard drive on the server. * It is more efficient to use session since with cookie the browser has to send all information with each and every request that it sends. With the session, all the information is setting on the server so the user does not have to send all the information each time it send a request. * Also, with sessions the data is more secure since it is stored on server.
Cons:
* The session is little bit slower since the request has to go to the browser and find the file and open it, with cookie the information is already available but the difference is usually not noticeable. * The session expires when browser is closed, while as the cookie will stay for as long as we want it to be stored. * The session file accumulate overtime since each session file is stored on the server so we need to clean up the server.
The session is stored on super global array. The syntax is: $_SESSION;. The sessions are stored in headers as cookies; therefore, it needs to be stored as the first thing in the html file. The reference to the session can be seen in cookie but it is a key which normally don’t make sense to users so we don’t have to have to worry about it being misused.
Connecting with mySql:
There are three mySql database APIs to connect to the database.
Mysql – original MySql API, mysqli – MySql ‘improved’ API, PDO – PHP data objects
These all three APIs do very similar job with small differences. PDO work with any database. But mysql and mysqli only work with mysql database. Mysql will be going away in sometime. Mysql does not support object oriented interface, mysqli and PDO do. So it is better to use mysqli.
There are five steps to connect to database:
1. Create a database connection
2. Perform database query
3. Use returned data (if any)
4. Release returned data
5. Close database connection
To connect to the database the command is: mysqli_connect($dbhost, $dbuser, $dbpass, $dbname);.
To check if database connection was successful, the command is: mysqli_connect_errno() – will tell us what is the error number, if there is no error it will be equal to zero. Mysqli_connect_error() – will tell us the error, if there is no error it will be empty string.
To close the database connection, the command is: mysqli_close($dbconnection_name);
Retrieving the data from database:
To query the data in mysql we can use command: mysqli_query($dbconnection_name, $our_query), to fetch data from database, we use command mysqli_fetch_row(), and to free up the data, we use command mysqli_free_result().