oral exam - Memory, References, and Parameters - mini

Describe pass by value

• A variable's value is copied and passed to the function.
  
  

• Changes to the parameter inside the function do not affect the original variable.
  
  

• Simple and easy to implement but inefficient for large data structures because copying is involved.
  
  

Example explanation:

• change(x) creates a copy of x
  
  

• Modifying the copy does not affect the original variable

Describe pass by reference

• Pass by reference allows a function to modify the original variable without copying it.
  
  

• The parameter becomes an alias for the original variable.
  
  

Key points:

1. int &num → num is a reference to the original variable
   
   

2. Any changes to num directly affect the original variable
   
   

Output example explanation:

Original variable value changes from 10 → 50 after function call

describe pointers

• Pointers store memory addresses of other variables.
  
  

• &var returns the memory address of var.
  
  

• Declaration: int* point_var;
  
  

Assigning addresses:

• int var = 5; int* point_var = &var;
  
  

Good practice: initialize pointers when declared

describe reference

• A reference variable is an alias for an existing variable.
  
  

• Created with & during declaration
  
  

Changing the reference changes the original variable

Compare and contrast pointers and references

Feature	Pointer	Reference
Definition	Stores memory address of another variable	Alias for an existing variable
Syntax	int *p;	int &r = x;
Initialization	Can be initialized later; can be null	Must be initialized; cannot be null

How is a pointer different from an ordinary variable?

• Ordinary variables store direct values
  
  

• Pointers store memory addresses
  
  

Pointers need * to dereference and access the value

Why is pass by reference often preferred over pass by value?

• Performance: avoids copying large objects (e.g., vectors, strings, custom classes)
  
  

• Efficient for large data structures with dynamic memory

Describe an advantage or disadvantage of pass by value

• Advantage: Simple, independent of original variable
  
  

• Disadvantage: Inefficient for large objects (copies data)

Describe an advantage or disadvantage of pass by reference

• Advantage: Modifies original variable without copying
  
  

Disadvantage: Changes original variable, can cause unintended side effects

Describe garbage collection

• Memory recovery feature in languages like Java
  
  

• Frees memory that is no longer needed, preventing memory exhaustion
  
  

C++ does not have built-in garbage collection

C++ has no mechanism for garbage collection. What does that mean for us as programmers?

• Must manually manage memory
  
  

• Allocate with new and free with delete
  
  

Can also use smart pointers or containers that manage memory automatically

Describe memory leaks and how they occur

• Occur when dynamically allocated memory is not freed
  
  

Memory remains reserved and cannot be reused, slowing the program or exhausting memory

Describe memory fragmentation and how it occurs

Causes:

• Frequent new/delete or malloc/free calls of different sizes
  
  

Types:

• External fragmentation: Free memory divided into small non-adjacent blocks
  
  

Internal fragmentation: Allocated block larger than needed

Describe paging/swapping

• swap() exchanges the values of two variables
  
  

Both variables must have the same data type

How, in C++, do we go about allocating and freeing up memory dynamically?

• Use malloc() or calloc() from <stdlib.h>
  
  

• malloc(size) → allocates memory
  
  

calloc(amount, size) → allocates multiple items, initialized to zero

Describe scope and how it affects variable visibility

• Variables are only accessible inside the region they are created
  
  

Local Scope:

• Variable inside a function, accessible only within that function
  
  

Global Scope:

• Variable outside all functions, accessible anywhere

When two objects declared in different scopes share the same name, which takes precedence? How do we retrieve the other?

• Innermost scope takes precedence → called variable shadowing
  
  

Use scope resolution operator :: to access outer/global variable

Describe default parameters. Where are they placed in a function?

• Default arguments are used if no value is provided during function call
  
  

• Must be on the right side
  
  

Recommended to specify in the function declaration (header)

What does a function’s type say about the function?

• Specifies the type of value returned by the function
  
  

Use void if no value is returned