PywE|PHP

Welcome!

Heya! In this course, we'll master PHP, a programming language that's used by millions of websites.

Let's hit the ground running and check out what this little PHP script does.

<?php
 echo "Welcome, friend!";
?>

//Output Below

Ah! In this lesson, we'll find out what we just did here.

Capabilities

PHP can do tons of things, making it a great choice for almost any website.

What might these things include?

It can take user input from forms
It can talk to databases
We can build dynamic webpages with it

Yes! That's why even big companies like Facebook and Tesla use PHP.

Echo-echo-echo

Do you remember the special word we used to display "Welcome, friend!"?

<?php  
echo "Welcome, friend!";
?>

//Output Below

That's it! The echo keyword displays, or prints, the plain text we put in the quotation marks after it.

Semicolons

Also, there's a special symbol at the end of every line.

What kind of symbol was that again?

<?php
 echo "Welcome, friend!";
?>

//Output Below

Yes! The semicolon tells the server that it can move to the next line.

Numbers

Apart from plain text, however, PHP can also handle numbers and do math with them.

<?php
 echo 2 * 4; 
?>

//Output Below

Magical! The * sign is an operator that multiplies two numbers. The + operator unsurprisingly, will add two numbers.

Psst: numbers have no quotation marks around them.

Variables

To create some more complex scripts, we need a way to remember information. So-called variables help us do just that.

<?php
$name = "Slim Shady";
 echo $name;
?>

//Output Below

Great! Variables start with a $ sign and have a name. We can pass them information using the = sign.

Comments

Comments are lines that can help us understand a script. We introduce them with two slashes.

<?php
// Create a variable and display its content:
 $name = "Slim Shady";
 echo $name;
?>

//Output Below

Perfect! When a line starts with //, it's ignored by the server.

A server-side language

Now, PHP is a so-called server-side language, which makes it different from languages like JavaScript.

Why might that be?

Any PHP script needs to run on a server
Only the results of a script are displayed in the browser

That's it! PHP scripts run on a server, which is the computer that stores them. Only the results are delivered to browser.

PHP and HTML

When we combine PHP with HTML, we can create dynamic webpages.

<html>
 <body>
  <?php
   echo "Hi, I'm written in PHP";
  ?>
 </body>
</html>

//Output Below

Yay! When we open this webpage, the server processes the script and sends only the output to the browser.

PHP files

If we include a PHP script in an HTML file, we need to save it with a .php extension.

Why might that be?

The extension tells the server that it needs to process the file

Right! The .php extension tells the server that there's PHP code in the file that it needs to process.

Variables

As we already know, variables are containers that can store information, or values to be precise.

<?php
$name = "Slim Shady";
?>

There! Now the $name variable stores the value "Slim Shady".

Strings

"Slim Shady" is a so-called string, a sequence of characters wrapped in single or double quotes.

<?php
 $first = 'Slim ';
 $second = "Shady";
 echo $first, $second;
?>

//Output Below

Slim Shady

See that? It doesn't matter if we use single or double quotes, as long as we want them to be part of the string.

Combining strings

We can do lots of fun things with strings. For example, we can add them together.

<?php
 $intro = "Hi, my name is ";
 $name = "Slim Shady";
 echo $intro . $name;
?>

//Output Below

Hi, my name is Slim Shady

Well said! The . sign is a so-called operator that combines the values of two or more strings.

Integers

Let's talk numbers. An integer is another data type that can represent whole numbers.

<?php
 $number = 720;
 echo $number;
?>

//Output Below

That's right! We've stored an integer, which can be positive or negative, in $number.

Floats

A float, or floating-point number, is a data type for numbers with a decimal point.

<?php 
 $number = 5.28;
 echo $number;
?>

//Output Below

5.28

Bingo! We've stored a float in $number. Just like integers, these values can be positive or negative.

Operators

We can use operators to do math with numbers.

Let's try and add these numbers.

<?php
 $number1 = 49;
 $number2 = 7;
 echo $number1 + $number2;
?>

//Output Below

See that? The + sign adds the numbers together just like a regular calculator.

Psst: The -, *, and \ signs also work exactly as you'd expect them to.

Shortcuts

If we want to in increase the value of a variable by, say, 10, we can use a shortcut.

<?php
 $number = 16;
 echo $number += 10;
?>

//Output Below

Perfect! +=, -=, *=, and /= give the result of the operation back to the variable.

Booleans

A boolean is a data type that can only be true or false.

Which of these might be the correct way to assign a boolean value?

<?php
 $boolean = true;
 echo $boolean;
?>

//Output Below

See that? When we use echo with a true boolean, 1 is printed. If the boolean were false, 0 would be printed.

Constants

Finally, constants are almost like variables, except that their values are, well, constant.

<?php
 define("PI", 3.1415926535898);
 echo PI;
?>

//Output Below

3.1415926535898

Yes! We don't need the $ sign with constants and usually write their names in uppercase letters.

Conditions

We can use so-called conditional statements to run a segment of a script only if a certain condition is met.

<?php
if (true) {
  echo "Hi there!";
}
?>

//Output Below

Hi there!

Fantastic! The code in the braces of an if statement only runs if its condition has the boolean value of true.

Comparison operators

That's why boolean values are so much more useful than they seem to be. For example, they're the result of comparisons.

Let's try and echo the statement here.

<?php
 $hour = 9;
 if ($hour < 12) {
  echo "Hello there!";
}
?>

//Output Below

Hello there!

See that? We can use > and < to check if a value is greater or less than another.

Equality

We can also check whether a value or variable is equal or not equal to something.

<?php
 $hour = 12;
 if ($hour == 12)
  echo "Equal!";
if ($hour != 1)
echo "Not equal!";  
?>

//Output Below

Equal!Not equal!

Perfect! The == and != signs are the comparison operators that check if two values are the same or not.

Else

Also, we can run code when the condition in the if statement isn't met. That's what we call an else statement.

<?php
 $hour = 12;
 if ($hour < 12) {
  echo "Good morning!";
 } else {
  echo "Good afternoon!";
 }
?>

//Output Below

Good afternoon!

Yes! The code in the braces of the else statement runs when the condition that comes before it returns false.

More comparison operators

Another set of comparison operators can check for equality and inequality at the same time.

<?php
 $hour = 20;
 if ($hour >= 18) {
  echo "Good evening!"; 
 }
?>

//Output Below

Good evening!

See that? The <= and >= signs check if a value is greater than or equal to or less than or equal to another value.

Elseif

We can also combine the else and if keywords to account for multiple conditions.

<?php
 $hour = 20;
 if ($hour < 12) {
  echo "Good morning!";
 } elseif ($hour < 18) {
  echo "Good afternoon!";
 } else {
  echo "Good evening!";
 }
?>

//Output Below

Good evening!

Bravo! The elseif keyword allows us to add as many conditions as we want to check for.

Logical operator &&

What if we want to test if two conditions are true at the same time, though? For that we use something called the logical and.

Which of these would satisfy what is either side of the &&?

<?php
 $hour = 12;
 if ($hour >= 0 && $hour < 24) {
  echo "Triggered!";   
 }  
?>

//Output Below

Triggered!

See that? && the logical and, needs both conditions met for the code inside to be executed.

Logical operator ||

When we want test if at least one condition is true, we use something called the the logical or.

Which of these would satisfy at least one condition either side of ||?

<?php
 $hour = 0;  
 if ($hour == 0 || $hour < 24) {
 echo "Triggered!";     
 }   
?>

//Output Below

Triggered!

Nice. || the logical or operator requires only one condition to be true in the statement for the code inside to be executed.

Switching

When we want to compare a variable with many different values, switch statements might be the better option.

Let's see what happens when we give $season a value here.

<?php
 $season = "Winter";
 switch ($season) {
  case "Winter";
   echo "Frozen season";
   break;
  case "Fall";
   echo "Cool season";
   break;
  default:
   echo "Other season";
 }
?>

//Output Below

Frozen season

See that? case checks for a scenario, break ends the code, and default triggers when there are no matches.

Free-falling

What if we want multiple cases in a switch statement to trigger the same code? In that case we group them together.

Which of these might trigger "You're not a freshman"?

<?php
 $year = 3;
 switch($year) {
  case 1:
   echo "You're a freshman";
   break;
  case 2:
  case 3:
  case 4:
   echo "You're not a freshman";
   break;
  default:
   echo "Are you still in school?";
 }
?>

//Output Below

You're not a freshman

See that? Cases without a break keyword will fall through to the next break keyword or to the end.

What's an array, you say?

An array is a special kind of variable that can store multiple values in a single variable.

<?php
 $friends = array();
?>

Huzzah! We just created an array with array(), the so-called array constructor.

Values

An empty array doesn't really serve a purpose, though. How about we give $friends some values?

<?php
 $friends = array("Caroline", "Max");
?>

Great! We can create an array with values by putting them in the parentheses of array().

Accessing

But how can we access the contents of an array?

<?php
 $friends = array("Caroline", "Max");
 echo $friends[0];
?>

//Output Below

Caroline

That's it! We can access a value by putting its position in brackets after the array's name.

Psst: this position is zero-based, which means that it starts at 0.

Adding

We can also add values to an array. Let's add something to $friends, shall we?

<?php
 $friends = array("Caroline", "Max");
$friends[] = "Earl";
?>

Nice! We can add a value by giving it to the array with brackets but without a position.

Replacing

Now that we know how to add values, how might we be able to replace one?

<?php
 $friends = array("Caroline", "Max");
 $friends[1]  = "Chestnut";
 var_dump($friends);
?>

//Output Below

array(2) {
 [0]=>
  string(8) "Caroline"
  [1]=>
  string(8) "Chestnut"
}

Fantastic! We can replace a value by storing a new value at a position that already exists.

Psst: var_dump() is a so-called function that displays information about a variable. It allows us to see the whole array.

Counting

We can find out the number of items in an array as well. How might we do this?

<?php
 $friends = array("Caroline", "Max");
 echo count($friends);
?>

//Output Below

Sweet! We can use the count() function to find out how many values an array has.

Sorting

We can also sort an array. Let's add some more values and get $friends in alphabetical order!

<?php
 $friends = array("Caroline",
  "Max", "Earl", "Oleg", "Han");
sort($friends);
 var_dump($friends);
?>

//Output Below

array(5) {
  [0]=>
  string(8) "Caroline"
  [1]=>
  string(4) "Earl"
  [2]=>
  string(3) "Han"
  [3]=>
  string(3) "Max"
  [4]=>
  string(4) "Oleg"
}

Right on! The sort() function orders the items of an array in ascending order, be they numbers or strings.

Psst: another function called rsort() sorts an array in descending order.

Looping

Sometimes we need to repeat a task over and over again.

<?php
 $friends = array("Caroline",
  "Max", "Earl", "Oleg", "Han");
 echo $friends[0] . ", ";
 echo $friends[1] . ", ";
 echo $friends[2] . ", ";
 echo $friends[3] . ", ";
 echo $friends[4];
?>

//Output Below

Caroline, Max, Earl, Oleg, Han

Look at all these lines of code! Might a loop be more readable without repeating ourselves?

While loops

A so-called while loop runs a block of code as long as a certain condition is true.

<?php
 $number = 1;
while ($number < 4) {
  $number += 1;
  echo $number . ", ";
 }
?>

//Output Below

2, 3, 4,

Yes! This while loop increases $number by 1 as long as it's less than 4. Once at 4, the condition turns false and the loop stops.

Do while loops

A do while loop is a type of while loop that first runs the block of code then checks if the condition is true.

<?php
 $number = 1;
 do {
  $number += 1;
  echo $number;
 } while ($number > 4);
?>

//Output Below

See that? No matter what the condition, the loop runs at least once.

Psst: notice that the do while loop ends with a semicolon.

For loops

The for loop is a very popular type of loop. It has 3 parts: the value, the condition, and a way to change the value.

<?php 
for ($i = 0; $i < 4; $i++) {
  echo $i . ", ";
 } 
?>

//Output Below

0, 1, 2, 3, 4,

Sweet! $i starts at 0 and increases as long as the condition is true. Once it returns false, the loop stops.

Psst: $i++ is an even shorter version of $i += 1.

Foreach loop

Now, the so-called foreach loop works only on arrays, because it goes through each of their elements.

<?php 
 $heroes = array("Batman", "Robin", "Batgirl"); 
 foreach ($heroes as $hero) {
  echo $hero . ", ";
 }
?>

//Output Below

Batman, Robin, Batgirl,

Nice! In every so-called iteration, the value of an element is stored in $hero.

Functions

A function is a block of code that we can reuse whenever we want.

<?php
function sayHi() {
  echo "Hi there!";
 }
?>

Nice! We need the function keyword, a name, and some parentheses. The code in the braces runs when we use the function.

Calling

But why didn't sayHi() display anything? Well, that's because we need to call a function to make it run.

<?php
 function sayHi() {
  echo "Hi there!";
 }
sayHi();
?>

//Output Below

Hi there!

Sweet! Whenever we want to call a function, we use its name and add parentheses at the end.

Arguments

We can also pass information to functions through arguments.

<?php
 function sayHi($name) {
  echo "Hi there, $name!";
 }
 sayHi("Joe");
?>

//Output Below

Hi there, Joe!

See that? When we use an argument with sayHi(), we can access it through $name variable.

Psst: notice how we can put variable names right into a string.

Returning

In addition to performing tasks, functions can return values as well.

<?php
 function sum($n1, $n2) {
  $sum = $n1 + $n2;
  return $sum;
 }
 echo "1 + 7 = " . sum(1, 7);
?>

//Output Below

1 + 7 = 8

Yes! We use the return keyword to give back a value whenever the function is called.

Managing strings

PHP has a lot of built-in functions as well. Some of them help us manage strings.

How might we convert a string to lowercase?

<?php
 echo strtolower("Here's the LOWDOWN.");
?>

//Output Below

here's the lowdown.

That's it! strtolower() will convert any string to lowercase.

Psst: strtoupper() will convert strings to uppercase.

Replacing characters

What if we want to replace characters in a string with other characters?

<?php
 $greeting = "Howdy y'all!"
 echo str_replace("y'all", "Joe", $greeting);
?>

//Output Below

Howdy Joe!

Great, right? str_replace() takes 3 arguments: the value to replace, its replacement, and the string it's in.

Psst: notice that str_replace() is case-sensitive.

Getting a substring

We can get part of a string with the substr() function.

It has 3 parts: the string, the index to start at, and the number of characters to get from there.

<?php
 $text = "You: a constant in the sea of variables.";
 echo substr($text, 0, 15);
?>

//Output Below

You: a constant

See that? We extract different parts of a string by changing the index and the number of characters to get.

Counting words

We can also count the number of words in a string with a built-in function.

<?php
 echo str_word_count("You: a constant in the sea of variables.");
?>

//Output Below

There! The str_word_count() function does the trick.

Rounding off numbers

Other built-in functions handle integers and floats.

How might we round a number?

<?php
 echo round(1.5);
?>

//Output Below

Fantastic! We can round a number with the round() function.

Exploding a string

Now, with the explode() function, we can spit a string into an array. It takes 2 arguments: a delimiter and a string.

<?php
 $game = "rock, paper, scissors";
 $items = explode(", ", $game);
 var_dump($items);
?>

Sweet! The delimiter is the string that separates the values in the original string.

Psst: var_dump(), of course, is also a function.

Welcome!

Capabilities

Tags

Echo-echo-echo

Semicolons

Numbers

Variables

Comments

A server-side language

PHP and HTML

PHP files

Variables

Strings

Combining strings

Integers

Floats

Operators

Shortcuts

Booleans

Constants

Conditions

Comparison operators

Equality

Else

More comparison operators

Elseif

Logical operator &&

Logical operator ||

Switching

Free-falling

What's an array, you say?

Values

Accessing

Adding

Replacing

Counting

Sorting

Looping

While loops

Do while loops

For loops

Foreach loop

Functions

Calling

Arguments

Returning

Managing strings

Replacing characters

Getting a substring

Counting words

Rounding off numbers

Exploding a string