C++ Pass-by-Reference: Why Use the & Symbol for Function Parameters?

### Why Use the & Symbol for Function Parameters? — The Secret of C++ Reference Passing This article explains the necessity of using the & symbol (reference passing) for function parameters in C++. By default, value passing copies a parameter's actual value, preventing the function from modifying the original variable (as seen in the swap function example where value passing fails). A reference is an "alias" for a variable, sharing the same memory with the original variable. When a function parameter is declared with &, it becomes a reference to the original variable, enabling direct modification of external variables. Advantages of reference passing include: directly modifying the original variable, avoiding the waste of copying large objects (e.g., structures, arrays), and resulting in cleaner code compared to pointer passing. It is crucial to distinguish the dual role of &: as the address-of operator (returns a pointer when used as &var) and as a reference declarator (e.g., int &a requires initialization and cannot change its target). Key notes: References must be initialized, cannot be null references, and their target cannot be changed once bound. Applicable scenarios include modifying external variables, handling large objects, and simplifying code. Reference passing uses the & symbol to achieve "direct operation on the original variable," solving the limitations of value passing and serving as a critical feature for efficiently modifying external variables.