How can conditional statements like "if(isset($returnValue))" be used to control the output of PHP functions based on the presence of a value?

Conditional statements like "if(isset($returnValue))" can be used to check if a variable has been set or has a value in PHP. This can be useful for controlling the output of functions based on whether a value exists or not. By using this conditional statement, you can ensure that certain actions are only taken if the variable has a value, preventing errors or unexpected behavior in your code.

// Check if $returnValue is set before using it
if(isset($returnValue)) {
    // Output the value of $returnValue
    echo $returnValue;
} else {
    // Output a default message if $returnValue is not set
    echo "No value set for returnValue";
}