PHP Basics: Syntax, Variables and Data Types

Now that you have written your first script, this lesson covers the PHP basics you will use in every file you ever write: how the syntax works, how to store values in variables, and which data types PHP gives you.

How PHP syntax works

PHP code lives inside <?php ... ?> tags. Anything outside them is sent to the browser untouched. That is why you can drop PHP straight into an HTML page.

<?php
  echo "This line comes from PHP";
?>

Output:

Two rules cover most of the syntax:

• Every statement ends with a semicolon.
• Variable names are case-sensitive But Keywords are not. Keywords like ECHO and echo both works, but $name and $Name are two different variables.

If your page suddenly loads blank, a missing semicolon is the usual reason.

Variables and constants

A variable is a labelled box. In PHP, every variable name starts with a dollar sign.

<?php
  $name  = "Flow";
  $age   = 22;
  $price = 9.99;
  echo "Hello, $name!";
  echo "<br>";
  echo "your Age is $age";
  echo "<br>";
  echo "and the price is $price"
?>

Output:

Notice that you never have to declare a type like int, char or float. PHP actually works that part out for you, and you can Assign Any Value Weather it is an int type value, float or character type and this value can be changed later because that's what variable's definition is right?

Variable: something that changes or can be changed...

A constant is the opposite of a variable: you set it once and it can never change. it stays fixed across the whole site, like a site name or a tax rate.

Now there are two ways to define a constant:

• via define function
• via keyword

Example:

<?php
  define("SITE_NAME", "Flow's Blog");
  const TAX_RATE = 0.17;
  echo SITE_NAME;
  echo "<br>";
  echo TAX_RATE;
?>

Output:

<?php
  define("SITE_NAME", "Flow's Blog");
  const TAX_RATE = 0.17;

  $price = 1000;
  $total = $price + ($price * TAX_RATE);

  echo SITE_NAME . " - order total: " . $total;
?>

Output:

Now try changing a constant after you have set it:

<?php
  const TAX_RATE = 0.17;

  TAX_RATE = 0.20;
?>

Output:

That error is PHP refusing to let a constant change, which is exactly what you want it to do.

One quoting rule matters a lot here. Double quotes read variables inside the string. Single quotes print them literally.

<?php
$name="Flow";
echo "Hello, $name";
echo 'Hello, $name';
?>

Output

<?php
$name="Flow";
echo 'Hello, $name';
?>

Output

The data types you will actually use

PHP has eight types in total. These six are the PHP basics you will meet every day.

• String — text, like "hello"
• Integer — whole numbers, like 42
• Float — decimals, like 9.99
• Boolean — true or false
• Array — a list of values in one variable
• NULL — deliberately empty

Use var_dump() when you want to see what PHP thinks a value is. It prints the type and the value together, which is far more useful than echo while you are learning.

<?php
  $price = 9.99;
  var_dump($price);
?>

Output

Putting the PHP basics together

Here is a short script that uses everything above.

<?php
  $product = "Notebook";
  $price   = 4.50;
  $inStock = true;
  $tags    = ["paper", "stationery"];

  echo "$product costs $price";

  if ($inStock) {
      echo " and it is in stock.";
  }
?>

Save it as basics.php, open it through your local server, then change a value and reload. Change it again. Breaking code teaches you more than reading it.

Three mistakes that catch everyone

Forgetting the dollar sign is the first one. name = "Flow" is not a variable in PHP.

The second is comparing with a single equals sign. = assigns a value, == compares two values, and === compares the value and the type.

The third is a missing closing quote. PHP usually blames a line further down, so check the line above the one it names.

What is next

You now have the PHP basics that real logic is built on. The next lesson puts them to work with if statements, loops, and functions. If you have not set up a local server yet, start with Introduction to PHP for Beginners. The full lesson list lives on the PHP tutorial hub.