Variables in PHP (Rules, Scope & Examples)

What is a variable

A variable is a named box in the computer's memory where you store a value so you can use it again later. In PHP every variable name starts with a dollar sign $. You put a value in with the = sign, and from then on the variable holds that value until you change it.

The special thing about PHP is that it is loosely typed — you never say whether a value is a number, text or true/false. You just assign it, and PHP works out the type on its own. This makes PHP quick to write and beginner-friendly.

Declaring variables

To create a variable, write $, then a name, then =, then the value. Here are a few of each common kind:

<?php
  $name  = "Aman";      // text (string)
  $age   = 18;          // whole number (integer)
  $price = 99.5;        // decimal number (float)
  $pass  = true;        // true/false (boolean)

  echo "$name is $age years old";
?>

Notice we did not tell PHP that $age is a number or $name is text — PHP figured that out from the value we assigned. Also, inside double quotes PHP replaces $name and $age with their values automatically.

Values a variable can hold

Because PHP is loosely typed, the same variable can change type. $x = 5; then later $x = "hello"; is perfectly allowed — though for clean code it is better to keep one kind of value in one variable.

Naming rules

• Must start with $ followed by a letter or an underscore — never a number.
• After that, letters, numbers and underscores are allowed ($user_1 is fine, $1user is not).
• No spaces and no special characters like - or @.
• Case-sensitive: $name and $Name are two different variables.
• Use meaningful names — $total_marks is far clearer than $t.

Variable scope

Scope means where a variable can be seen. A variable made inside a function is local — it does not exist outside that function. A variable made outside is global.

<?php
  $site = "CodingEasily";   // global

  function show() {
      echo $site;           // ERROR: not visible here
  }

  function showRight() {
      global $site;         // now it is visible
      echo $site;
  }
  showRight();
?>

By default a function cannot see outside variables. To use one, either pass it in as a parameter (the clean way) or bring it in with the global keyword.

Common mistakes

• Forgetting the $. Writing name = "Aman" instead of $name = "Aman" causes an error.
• Case mismatch. Setting $Name but reading $name gives an undefined-variable warning.
• Using = in a condition. if ($x = 5) assigns instead of comparing — use ==.
• Using a variable before assigning it. Always give a starting value first.

Summary

• Every PHP variable starts with $ and stores a value with =.
• PHP is loosely typed — you never declare the type; PHP decides it.
• Names are case-sensitive and must start with a letter or underscore.
• = assigns, == compares — keep them separate.
• Function variables are local unless passed in or marked global.

Next, learn what kinds of values exist in detail in PHP data types, or make decisions with if-else in PHP.