How can undefined constant or variable errors be identified and resolved in PHP?

Undefined constant or variable errors in PHP can be identified by checking the error message provided by PHP when the error occurs. To resolve these errors, ensure that all constants are defined using the `define()` function and variables are initialized before being used in the code. Example PHP code snippet: 

// Define a constant
define('PI', 3.14);

// Initialize a variable
$radius = 5;

// Calculate the area of a circle
$area = PI * ($radius ** 2);

echo "The area of the circle is: " . $area;

Keywords

PHP constant variable error debugging

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