What are some common pitfalls when trying to pass variables between functions in PHP?

One common pitfall when passing variables between functions in PHP is not properly defining the variable scope. To ensure variables are accessible within multiple functions, you can use global variables or pass them as parameters to the functions. Another pitfall is not returning or assigning the modified variable back to the calling function.

// Using global variables to pass variables between functions
$globalVar = "Hello";

function modifyGlobalVar() {
    global $globalVar;
    $globalVar .= " World";
}

modifyGlobalVar();
echo $globalVar; // Output: Hello World