What is the significance of the concatenation operator (.) used in the modified PHP code snippet?

The concatenation operator (.) in PHP is used to combine two strings together. In the modified PHP code snippet, the issue may be that the variables are not being concatenated correctly, resulting in unexpected output. To solve this issue, the concatenation operator should be used to properly combine the variables and strings.

// Original code snippet
$firstName = "John";
$lastName = "Doe";
echo "Hello, $firstName $lastName!";

// Modified code snippet with concatenation operator
$firstName = "John";
$lastName = "Doe";
echo "Hello, " . $firstName . " " . $lastName . "!";