What are the common reasons for encountering the "Undefined variable" error in PHP code?

The "Undefined variable" error in PHP code occurs when a variable is used without being declared or initialized beforehand. To solve this issue, make sure to define the variable before using it in your code. You can either assign a value to the variable or initialize it as an empty value such as an empty string or array.

// Example of fixing the "Undefined variable" error
$variable = ""; // Initialize the variable with an empty string

// Now the variable can be used without encountering the error
echo $variable;