PHP type juggling refers to the dynamic system where the type of a variable is determined by its context in the operation. You don’t need to explicitly declare types for your variables, but take care; it introduces potential security vulnerabilities.

In other words, during program translation, there are some defined variables with their data types that change to another type through the program compilation.

Also, this concept refers to the arithmetic that is already written in the first letter of a string data type value and calculated with another integer data type value.

Let’s see how it works with PHP code examples.

How PHP Type Juggling Works Behind the Scenes

The following example shows you that the first data type for the PHP variable was an integer value.

$value = 150;
echo gettype($value); // integer

In the code below, you will see a variable declaration, followed by its direct conversion into an array.

$value = 150;
$value = array(150);
echo gettype( $value ); // array

So, that is happening in the program execution to change the variable value into another or assign a new boolean type or whatever to be proper for some operations in the program stack. Such as storing new data in the same variable, changing the old value to another, and so on.

In the following section, I am going to explain what is happening in the arithmetic operations during the compilation if the string value is calculated with an integer value.

PHP Type Juggling with Comparison Operators

The PHP type of juggling has two comparison modes, as shown in the following list.

  • The strict operators (===).
  • The loose operators (==).

The first one is for detecting value and type, but on the other hand, the second one makes the checking easier by only checking for the value. Let’s see that.

In the next example, I will compare a string variable with another integer data type using a loose comparison.

  $string  = "105";
  $integer = 105;
  if ( $string == $integer ) {
    echo "Correct Result";
  } else {
    echo "Not Correct !";

The output of this example would be – “Correct Result”.

Essentially, PHP automatically converts one of the two variables to be the same data type as the other one. So, as you saw in the previous example, we have a variable with a string data type and another one with an integer data type.

In the program compilation, it starts the casting automatically to convert the string value to an integer data type, and once it compares the two values, it will give you identical true values. Also, this process is called PHP-type juggling.

In the following section, I am going to discuss how the arithmetic operator works behind the scenes under the cover of PHP-type juggling.

Arithmetic Operations Cases

In the previous section, we explained the automatic conversion during the compilation. And here we have the same concept in arithmetic operations.

For a quick example.

  $string  = "10";
  $integer =  100;
  $calcs   = $string * $integer;
  echo $calcs;
  echo "\n";
  echo gettype($calcs);

The output would be like the one below.


In the next example, we will use string numbers and sum them with another integer value.

  $calc_1 = "105" + 15;
  echo $calc_1; // 15

Anyway, let’s summarize it.

Wrapping Up

PHP type juggling is a dynamic system that determines the variable’s type based on its context within an operation.

So during program translation, defined variables with specific data types can change to another type through program compilation. This concept extends to arithmetic operations involving string and integer data types, demonstrating PHP’s flexibility.

In the above examples, you understood how PHP automatically converts data types during operations.

Thank you for reading. Happy Coding!