What is the difference between pass-by-value and pass-by-reference?

The distinction between pass-by-value and pass-by-reference is fundamental in understanding how data is handled in programming, particularly in C++. When a function is called, arguments can be passed in different ways, influencing the function's ability to modify the original data.

Pass-by-value involves sending a copy of the variable's value into the function. This means that any modifications made to the variable inside the function do not affect the original variable outside the function. Each function call operates on its own copy of the variable, ensuring that the original data remains unchanged.

On the other hand, pass-by-reference means that the function receives a reference, or an alias, to the original variable. This allows the function to access and manipulate the actual variable, meaning any changes made within the function will directly affect the original variable. This technique is particularly useful when working with large data structures, as it avoids the overhead of copying large amounts of data.

Thus, the correct answer highlights that pass-by-reference allows for the original variable to be accessed and modified directly, distinguishing it clearly from the pass-by-value method. This understanding is essential for effectively managing memory and data flow within C++ programs.