11: Pointers and Linked Lists

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Questions and Answers

What is a key difference between references and pointers?

References cannot be null.

Pointers can point to no object. (correct)

References can be modified after creation.

Pointers cannot be changed after creation.

A null-pointer can be dereferenced safely without causing an error.

False

What keyword is used to represent a null-pointer in C++?

nullptr

A pointer to an int is declared as _____.

int* Signup and view all the answers

Match the following terms with their definitions:

Pointer = A variable that holds the address of another variable Null-pointer = A special pointer that signals no object points to it Dereferencing = Accessing the value at the address held by a pointer Pointer type = Defined by T* where T is a data type Signup and view all the answers

What will happen if you try to initialize a std::string pointer with an int pointer?

It will result in a compiler error. Signup and view all the answers

Why is it important to check if a pointer is nullptr before dereferencing it?

To avoid undefined behavior and potential runtime errors. Signup and view all the answers

What is a key advantage of using a linked list over a vector?

Easy insertion and deletion of elements Signup and view all the answers

Linked lists provide efficient random access to elements.

False Signup and view all the answers

What is the main component of a linked list?

lnode Signup and view all the answers

A linked list consists of nodes that contain user data and a pointer to the ______.

next element Signup and view all the answers

Match the following terms related to linked lists with their definitions:

lnode = A structure containing user data and a pointer to the next element Insertion = Adding an element to the linked list Deletion = Removing an element from the linked list Head = Pointer to the first element in a linked list Signup and view all the answers

Which of the following describes a linked list?

Supports efficient insertion and deletion Signup and view all the answers

An lnode can only contain an integer value.

False Signup and view all the answers

What does the 'next' pointer in an lnode do?

Points to the next lnode Signup and view all the answers

A linked list does not require a ______ area of memory.

contiguous Signup and view all the answers

What is a potential downside of writing overly compact code?

It may be difficult for others to comprehend. Signup and view all the answers

Using a second pointer, tail, in a list data structure can improve the efficiency of operations like push_back.

True Signup and view all the answers

What mechanism can be implemented to efficiently return the size of a list without traversing it?

Maintain a member variable to keep track of the list size. Signup and view all the answers

In a linked list implementation, the pointer that points to the first element is called the _______.

head Signup and view all the answers

Match the following linked list variations with their advantages or characteristics:

Singly linked list = Simple structure, only one pointer per node Doubly linked list = Allows traversal in both directions Linked list with sentinels = Simplifies edge cases for empty lists Circular linked list = Last node points back to the first node Signup and view all the answers

What is the purpose of the `our_list` class?

To wrap a pointer to the first element and manage list operations. Signup and view all the answers

The `push_front` method modifies the value of the head pointer to point to the newly added node.

True Signup and view all the answers

What does the `print` member function do?

Outputs the value of each element in the linked list. Signup and view all the answers

In the `our_list::push_front` method, the new element is initialized with a value of ______ and the next pointer to the current head.

4 Signup and view all the answers

Match the methods with their functionalities in the `our_list` class:

print = Outputs element values of the linked list push_front = Adds a new node at the front size = Returns the number of elements in the list push_back = Adds a new node at the end Signup and view all the answers

What could happen if the for-loop in the `print` function iterates beyond the valid nodes?

It will result in undefined behavior. Signup and view all the answers

The `head` pointer in the `our_list` class points to the last element of the list.

False Signup and view all the answers

What type is the `next` pointer in the `lnode` structure?

lnode* Signup and view all the answers

The implementation of the `print` function uses a ______ loop to iterate through the linked list.

for Signup and view all the answers

What type of data structure does the `our_list` class represent?

Linked list Signup and view all the answers

What will happen if a new lnode is not allocated dynamically in the push_front method?

It will lead to undefined behavior. Signup and view all the answers

The constructor of our_list initializes the head to nullptr.

True Signup and view all the answers

What should be checked in the push_back implementation before accessing n->next?

Check if head is nullptr. Signup and view all the answers

In the push_back implementation, if the list is not empty, we traverse to the end by using a _________ loop.

for Signup and view all the answers

Match the following implementations with their descriptions:

Example 16.2 = A buggy implementation of push_back Example 16.3 = A correct implementation of push_back Example 16.4 = A compact version using double-pointers Constructor = Initializes the list with a given size Signup and view all the answers

Which case checks for an empty list in the push_back method?

Case 1: Empty list Signup and view all the answers

The implementation of push_back in Example 16.3 handles the empty list case correctly.

True Signup and view all the answers

What is one possible drawback of using the implementation in Example 16.4?

It is less explicit and harder to understand. Signup and view all the answers

The implementation of dynamic data structures requires taking all possible ______ into account.

cases Signup and view all the answers

What is the purpose of the push_front method?

To add an element at the beginning of the list. Signup and view all the answers

What member function of the `our_list` class provides an iterator to the last element plus one?

end() Signup and view all the answers

The `operator[]` in the `our_list` class allows for random access to elements in the list.

False Signup and view all the answers

What does the `operator++` function do in the context of the `our_list` iterator?

Advances the iterator to the next element. Signup and view all the answers

The `our_list::begin()` function returns an iterator pointing to the ______ element.

first Signup and view all the answers

Match the following operations with their descriptions in the context of `our_list`:

begin() = Returns an iterator to the first element. end() = Returns an iterator past the last element. operator*() = Accesses the current element pointed to by the iterator. operator++ = Advances the iterator to the next element. Signup and view all the answers

What is the main issue with the first attempt to create a wagon structure?

The field 'next' has an incomplete type. Signup and view all the answers

A pointer must always be initialized at the time of its declaration.

False Signup and view all the answers

What type does the 'next' member of a wagon in C++ need to be, in order to form a linked list?

wagon* Signup and view all the answers

To create a new wagon in C++, one needs to use the _______ expression.

new Signup and view all the answers

Which of the following examples correctly declares a pointer to an integer?

int* p; Signup and view all the answers

Match the pointer types with their descriptions:

int* = Pointer to an integer std::string* = Pointer to a string wagon* = Pointer to a wagon object void* = Pointer to any type Signup and view all the answers

The 'next' pointer in a wagon structure can point to a newly created wagon or be set to nullptr.

True Signup and view all the answers

What is one advantage of linked lists over vectors in C++?

Dynamic size and efficient insertions/deletions. Signup and view all the answers

What happens if the list is empty when the push_back method is called?

The program results in undefined behavior. Signup and view all the answers

The push_back method handles the empty list case correctly by checking if head is nullptr.

True Signup and view all the answers

What is maintained as a member variable to improve efficiency in getting the size of the list?

count Signup and view all the answers

In the push_back method, the ____ pointer is used to point directly to the last element of the list for efficiency.

tail Signup and view all the answers

What will the size function return if the list is empty?

0 Signup and view all the answers

Dereferencing a nullptr in the push_back implementation will not cause an error.

False Signup and view all the answers

What is the initial value of count when using the simple size implementation?

0 Signup and view all the answers

The push_back method appends a new element to the list by setting n->next to a new lnode containing the value of _____.

e Signup and view all the answers

Which of the following methods is considered inefficient for calculating the size of our_list?

Iterating through the linked list Signup and view all the answers

What does the operator* do in the our_list iterator?

Accesses the current element Signup and view all the answers

The operator++ increases the iterator by one and returns a reference to the iterator itself.

True Signup and view all the answers

What is the purpose of the begin() member function in the our_list class?

To return an iterator pointing to the first element of the list. Signup and view all the answers

An iterator can be compared to another iterator using the operator ______.

!= Signup and view all the answers

Match the iterator functionality with its description:

operator++ = Advances the iterator to the next element operator*() = Accesses the current element value operator!= = Checks if two iterators are not equal Signup and view all the answers

What type of pointer does the lnode structure have?

A pointer to the next lnode Signup and view all the answers

The operator++ method does not need to check if the current node is nullptr.

False Signup and view all the answers

Which of the following describes a key characteristic of a linked list?

Each element points to its successor. Signup and view all the answers

The 'push_front' method allows easy removal of the first element in a linked list.

False Signup and view all the answers

What does the constructor of our_list::iterator initialize its member variable, 'node', to?

It initializes it to the lnode pointer passed as an argument. Signup and view all the answers

What does the 'next' pointer in an lnode structure do?

It points to the next node in the linked list. Signup and view all the answers

The our_list::iterator class is defined as a ______ class within the our_list class.

public inner Signup and view all the answers

In the implementation of the our_list constructor, head is initialized to _____ to indicate an empty list.

nullptr Signup and view all the answers

What does the end() member function of our_list return?

An iterator pointing past the last element Signup and view all the answers

Match the linked list methods with their functionalities:

push_front = Adds an element to the front of the list push_back = Adds an element to the end of the list print = Displays the elements of the list our_list = Constructor for the linked list Signup and view all the answers

What is a disadvantage of using linked lists compared to arrays?

Traversal requires more time due to non-contiguous memory. Signup and view all the answers

Dynamic allocation of nodes is necessary for the 'push_front' method to ensure data isn't lost after method execution.

True Signup and view all the answers

How does the 'print' function identify when to stop traversing the list?

It checks for a nullptr pointer. Signup and view all the answers

The linked list structure includes a node type called _____ that contains an integer value and a pointer to the next node.

lnode Signup and view all the answers

Which operation in linked lists is typically less efficient and requires traversal from the head?

Inserting an element at the end with push_back Signup and view all the answers

What is the purpose of the dereference operator (*) in pointer usage?

To access the value at the memory address the pointer points to Signup and view all the answers

A pointer can point to multiple types of objects at the same time.

False Signup and view all the answers

What keyword is used to initialize a pointer without a starting value?

nullptr Signup and view all the answers

To obtain the address of a variable, the _______ operator is used.

& Signup and view all the answers

Match the pointer operations with their descriptions:

ptr = nullptr = Initializes the pointer without a valid target. *ptr = 5 = Sets the value at the memory location to 5. ptr = &a = Makes the pointer point to the address of variable a. ptr == other_ptr = Compares if both pointers point to the same address. Signup and view all the answers

When declaring a pointer, what must the type of the pointer match?

The type of the variable it will point to Signup and view all the answers

The statement `int* ptr = &a;` is valid if a is an integer variable.

True Signup and view all the answers

What will happen if you try to dereference a nullptr pointer?

It will cause a runtime error. Signup and view all the answers

Study Notes

Introduction to Computer Science

Course numbers: 252-0032, 252-0047, 252-0058
Authors: Manuela Fischer and Felix Friedrich
Department: Computer Science, ETH Zurich
Semester: Fall 2024

Pointers and Dynamic Memory

Dynamic memory involves allocating memory during program execution.
Pointers store memory addresses, allowing access to the data stored there.
Wagons in a train, for example, can be linked using pointers.
References cannot be reassigned and require initialization when declared.
Pointers can be modified after creation.
A pointer to a type T, declared as T*, is used to store the memory address of an object of type T.
The address operator (&) finds the memory address of a variable.
The dereference operator (*) accesses the value stored at a memory address stored by a pointer.
Null pointers represent situations where a pointer does not point to a valid object.
Null pointers are denoted by the literal nullptr.
The null pointer cannot be dereferenced.
Using pointers to represent linked structures requires careful consideration of potential runtime errors due to incorrect operations on pointers when the list is empty.
Const pointers, which are pointers to constant values, are used to prevent modification of the pointed-to data.

Dynamic Data Structures

Linked lists are data structures where elements are not stored contiguously in memory but are linked together.
Linked lists allow efficient insertion and deletion of elements.
Random access is not efficient in linked lists.
Lists can be implemented in terms of elements that point to succeeding elements.
The nodes contain data elements and pointers to the next node.
The head node points to the first node.
Linked lists can store any type of data.
Code examples are provided that demonstrate how to create, manipulate, and traverse linked lists.
The implementation of operations like push_back must handle cases where the list is empty to avoid errors.
Dynamic memory allocation with new is used to allocate memory during program execution for these structures.
std::list is a container implemented using linked lists.
Iterators are used to systematically traverse and access elements within linked lists.
Iterators need methods like operator*(), operator++(), and operator!=() for dereferencing, advancing, and checking to end.
Member functions like begin() and end() on the list class provide iterators to the start and end of the list.
Using double pointers (`lnode** target*/) can lead to more compact code, but less readability.
Invariants and corner cases (such as empty lists) need to be considered when implementing linked list functions.
Iterators can be used with algorithms from the standard library.
Range-based for loops can be used with iterators.

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11: Pointers and Linked Lists

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Questions and Answers

What is a key difference between references and pointers?

A null-pointer can be dereferenced safely without causing an error.

What keyword is used to represent a null-pointer in C++?

A pointer to an int is declared as _____.

Match the following terms with their definitions:

What will happen if you try to initialize a std::string pointer with an int pointer?

Why is it important to check if a pointer is nullptr before dereferencing it?

What is a key advantage of using a linked list over a vector?

Linked lists provide efficient random access to elements.

What is the main component of a linked list?

A linked list consists of nodes that contain user data and a pointer to the ______.

Match the following terms related to linked lists with their definitions:

Which of the following describes a linked list?

An lnode can only contain an integer value.

What does the 'next' pointer in an lnode do?

A linked list does not require a ______ area of memory.

What is a potential downside of writing overly compact code?

Using a second pointer, tail, in a list data structure can improve the efficiency of operations like push_back.

What mechanism can be implemented to efficiently return the size of a list without traversing it?

In a linked list implementation, the pointer that points to the first element is called the _______.

Match the following linked list variations with their advantages or characteristics:

What is the purpose of the our_list class?

The push_front method modifies the value of the head pointer to point to the newly added node.

What does the print member function do?

In the our_list::push_front method, the new element is initialized with a value of ______ and the next pointer to the current head.

Match the methods with their functionalities in the our_list class:

What could happen if the for-loop in the print function iterates beyond the valid nodes?

The head pointer in the our_list class points to the last element of the list.

What type is the next pointer in the lnode structure?

The implementation of the print function uses a ______ loop to iterate through the linked list.

What type of data structure does the our_list class represent?

What will happen if a new lnode is not allocated dynamically in the push_front method?

The constructor of our_list initializes the head to nullptr.

What should be checked in the push_back implementation before accessing n->next?

In the push_back implementation, if the list is not empty, we traverse to the end by using a _________ loop.

Match the following implementations with their descriptions:

Which case checks for an empty list in the push_back method?

The implementation of push_back in Example 16.3 handles the empty list case correctly.

What is one possible drawback of using the implementation in Example 16.4?

The implementation of dynamic data structures requires taking all possible ______ into account.

What is the purpose of the push_front method?

What member function of the our_list class provides an iterator to the last element plus one?

The operator[] in the our_list class allows for random access to elements in the list.

What does the operator++ function do in the context of the our_list iterator?

The our_list::begin() function returns an iterator pointing to the ______ element.

Match the following operations with their descriptions in the context of our_list:

What is the main issue with the first attempt to create a wagon structure?

A pointer must always be initialized at the time of its declaration.

What type does the 'next' member of a wagon in C++ need to be, in order to form a linked list?

To create a new wagon in C++, one needs to use the _______ expression.

Which of the following examples correctly declares a pointer to an integer?

Match the pointer types with their descriptions:

The 'next' pointer in a wagon structure can point to a newly created wagon or be set to nullptr.

What is one advantage of linked lists over vectors in C++?

What happens if the list is empty when the push_back method is called?

The push_back method handles the empty list case correctly by checking if head is nullptr.

What is maintained as a member variable to improve efficiency in getting the size of the list?

In the push_back method, the ____ pointer is used to point directly to the last element of the list for efficiency.

What will the size function return if the list is empty?

Dereferencing a nullptr in the push_back implementation will not cause an error.

What is the initial value of count when using the simple size implementation?

The push_back method appends a new element to the list by setting n->next to a new lnode containing the value of _____.

Which of the following methods is considered inefficient for calculating the size of our_list?

What does the operator* do in the our_list iterator?

The operator++ increases the iterator by one and returns a reference to the iterator itself.

What is the purpose of the begin() member function in the our_list class?

An iterator can be compared to another iterator using the operator ______.

Match the iterator functionality with its description:

What type of pointer does the lnode structure have?

The operator++ method does not need to check if the current node is nullptr.

Which of the following describes a key characteristic of a linked list?

The 'push_front' method allows easy removal of the first element in a linked list.

What does the constructor of our_list::iterator initialize its member variable, 'node', to?

What does the 'next' pointer in an lnode structure do?

The our_list::iterator class is defined as a ______ class within the our_list class.

In the implementation of the our_list constructor, head is initialized to _____ to indicate an empty list.

What is the purpose of the `our_list` class?

The `push_front` method modifies the value of the head pointer to point to the newly added node.

What does the `print` member function do?

In the `our_list::push_front` method, the new element is initialized with a value of ______ and the next pointer to the current head.

Match the methods with their functionalities in the `our_list` class:

What could happen if the for-loop in the `print` function iterates beyond the valid nodes?

The `head` pointer in the `our_list` class points to the last element of the list.

What type is the `next` pointer in the `lnode` structure?

The implementation of the `print` function uses a ______ loop to iterate through the linked list.

What type of data structure does the `our_list` class represent?

What member function of the `our_list` class provides an iterator to the last element plus one?

The `operator[]` in the `our_list` class allows for random access to elements in the list.

What does the `operator++` function do in the context of the `our_list` iterator?

The `our_list::begin()` function returns an iterator pointing to the ______ element.

Match the following operations with their descriptions in the context of `our_list`:

The statement `int* ptr = &a;` is valid if a is an integer variable.