How do you declare variables and assign values in PHP? Provide examples.

In PHP, declaring variables and assigning values to them is a fundamental concept. Variables are used to store data that can be accessed and manipulated throughout the program. Here's an in-depth explanation of how to declare variables and assign values in PHP:

To declare a variable in PHP, you start with a dollar sign (`$`) followed by the variable name. Variable names are case-sensitive and can consist of letters, numbers, and underscores. However, they must start with a letter or an underscore. Here's an example of declaring a variable:

```
php`$name;`
```
In the above example, we have declared a variable named `$name` without assigning it any value. It is important to note that PHP does not require explicit type declaration for variables. The type of a variable is dynamically determined based on the value assigned to it.

To assign a value to a variable, you use the assignment operator (`=`). The value can be of any data type, such as a string, number, boolean, or even an array. Here are some examples of assigning values to variables:

```
php`$name = "John Doe"; // Assigning a string value
$age = 25; // Assigning an integer value
$price = 9.99; // Assigning a float value
$isReady = true; // Assigning a boolean value`
```
In the examples above, we assigned different values to variables. `$name` stores a string value, `$age` stores an integer value, `$price` stores a float value, and `$isReady` stores a boolean value.

It's worth mentioning that PHP is a loosely typed language, meaning variables can change their type during runtime. For instance, a variable initially assigned a string value can later be reassigned a numeric value without explicitly specifying its type.

You can also assign the value of one variable to another variable. This is called variable assignment by reference. Here's an example:

```
php`$number = 10;
$copyOfNumber = $number; // Assigning the value of $number to $copyOfNumber`
```
In the example above, the value of `$number` (which is 10) is assigned to `$copyOfNumber`. Any subsequent changes to `$number` will not affect `$copyOfNumber` since it is a separate copy of the value.

In summary, declaring variables in PHP involves using the `$` symbol followed by the variable name. Assigning values to variables is done using the assignment operator (`=`), and the value can be of any data type. Variables in PHP are dynamically typed, meaning their types can change during runtime.