13: Dynamic Data Structures II
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Questions and Answers

What operator is used to allocate memory for a block of objects in dynamic arrays?

  • malloc
  • alloc
  • new (correct)
  • calloc

    • A static array must have its size determined at runtime.

    False

    In dynamic data structures, where do the elements of a vector reside?

    heap

    To create a dynamic array of objects of type T with length n, the expression is new T[____].

    <p>n</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Dynamic Array = A memory structure that can change size during runtime Static Array = A memory structure with a fixed size determined at compile-time Heap = Memory used for dynamic storage and allocation Stack = Memory used for static storage</p> Signup and view all the answers

    Which operation retrieves an element from a vector?

    <p>v[i]</p> Signup and view all the answers

    The size of a vector can remain constant during its lifetime.

    <p>False</p> Signup and view all the answers

    What does the push_back operation do in a vector?

    <p>appends an element</p> Signup and view all the answers

    A contiguous part of memory allocated for storing dynamic arrays is referred to as an _______.

    <p>array</p> Signup and view all the answers

    What is the result of allocating every element of a vector separately?

    <p>Elements being spread out in memory</p> Signup and view all the answers

    What does the new T[] operator return?

    <p>A pointer to the first element of the array</p> Signup and view all the answers

    Pointer arithmetic allows you to access elements beyond the bounds of the array.

    <p>False</p> Signup and view all the answers

    What segments of memory does a pointer point to when using the new T[] operator?

    <p>The starting address of the allocated memory chunk for the array.</p> Signup and view all the answers

    To access the third element of an array pointed to by pointer p, you would use *(p + ______).

    <p>2</p> Signup and view all the answers

    Match the pointer expressions with their corresponding descriptions.

    <p>p + 0 = Points to the first element p + n - 1 = Points to the last element p + n = Points one beyond the last element *(p + i) = Accesses the value at index i</p> Signup and view all the answers

    If int* p = new int[n]; how do you access the value of the second element?

    <p>*(p + 1)</p> Signup and view all the answers

    The expression p + 3 directly gives you the address of the first element in the array.

    <p>False</p> Signup and view all the answers

    In the context of pointer arithmetic, what does 'p + i' represent?

    <p>The address of the (i + 1)th element in the array.</p> Signup and view all the answers

    If p points to an integer array of size n, then p + n points to ______.

    <p>one past the last element</p> Signup and view all the answers

    What happens if you try to access *(p + n)?

    <p>It results in a runtime error.</p> Signup and view all the answers

    What is the purpose of the push_back operation in a vector?

    <p>Append an element to the end of the vector.</p> Signup and view all the answers

    The new operator is used to allocate memory for a fixed size array at compile time.

    <p>False</p> Signup and view all the answers

    What does the expression *(p + i) yield?

    <p>The value of the ith element in the array.</p> Signup and view all the answers

    The chunk of memory allocated for dynamic arrays is called an __________.

    <p>array</p> Signup and view all the answers

    Match the following pointer expressions with their descriptions:

    <p>p = Points to the first array element p + 3 = Points to the fourth element *(p + i) = Retrieves the value of the ith element p + n = Points to the address after the last element</p> Signup and view all the answers

    What is the value of *(p + 2) if int* p = new int[5] and we initially set the array values to {10, 20, 30, 40, 50}?

    <p>30</p> Signup and view all the answers

    Pointer arithmetic allows access to elements only within the bounds of the allocated array.

    <p>False</p> Signup and view all the answers

    A vector is a static data structure that must have its size determined at compile time.

    <p>False</p> Signup and view all the answers

    What is the expression used to allocate a new array of size n for type T?

    <p>new T[n]</p> Signup and view all the answers

    In pointer arithmetic, the expression *(p + i) yields the value of the ______ element.

    <p>i-th</p> Signup and view all the answers

    Match the following pointer operations with their effects:

    <p>p + n = Points to the address just past the last element *p = Dereferences to the first element of the array *(p + 2) = Accesses the third element of the array p - 1 = Points to the address before the first element</p> Signup and view all the answers

    After allocating an array with the expression int* p = new int[5], what will p + 2 point to?

    <p>The address of the third element</p> Signup and view all the answers

    Pointer arithmetic allows you to access elements beyond the allocated memory of an array.

    <p>False</p> Signup and view all the answers

    What type of pointer is returned when using the new T[n] expression?

    <p>T* (pointer to type T)</p> Signup and view all the answers

    By using the expression new T[____], a contiguous block of memory can be allocated dynamically.

    <p>n (where n is a positive integer)</p> Signup and view all the answers

    Match the following components of a vector with their descriptions:

    <p>v.size() = Returns the current number of elements in the vector v[i] = Retrieves the element at index i v.push_back(e) = Adds element e to the end of the vector e = v[i] = Assigns the value of the ith element to e</p> Signup and view all the answers

    What must be done before accessing an array's elements?

    <p>Ensure indices do not exceed the array's bounds.</p> Signup and view all the answers

    Arrays can be copied directly using assignment.

    <p>False</p> Signup and view all the answers

    What operator is used to delete a dynamically allocated array?

    <p>delete[]</p> Signup and view all the answers

    When using arrays, the programmer must ensure that the indices do not go __________.

    <p>out of bounds</p> Signup and view all the answers

    Match the programming commands with their descriptions:

    <p>new int[n]; = Allocates a new array with size n. delete[] range; = Deallocates a dynamically allocated array. ptr + 3; = Shifts the pointer temporarily. ++ptr; = Moves the pointer to the next element permanently.</p> Signup and view all the answers

    What happens if you attempt to access an index that is out of the array's bounds?

    <p>It may result in undefined behavior.</p> Signup and view all the answers

    The length of an array must be specified at runtime.

    <p>False</p> Signup and view all the answers

    What is the initial value of array indices in programming?

    <p>0</p> Signup and view all the answers

    In pointer arithmetic, to access the fifth element using pointer p, you would use *(p + __________).

    <p>4</p> Signup and view all the answers

    Match the following array operations with their results:

    <p>a[i] = b[i]; = Element-wise copying of arrays. delete range; = Incorrect deletion of dynamically allocated memory. ptr1 &lt; ptr2; = Compares the positions of two pointers. ptr++; = Advances the pointer to the next memory location.</p> Signup and view all the answers

    Study Notes

    Introduction to Computer Science Course Information

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

    Dynamic Data Structures II, Section 17

    • Dynamic allocation of memory for objects using 'new'
    • Implementing a vector class named 'our_vector' (equivalent to std::vector)
    • Vectors allow dynamic resizing
    • Memory contiguity in vectors
    • Dynamic arrays
    • Allocating memory chunks using new T[n] for n objects of type T
    • Pointer arithmetic
      • Adding an integer to a pointer
      • Pointer differences
      • Subtracting an integer from a pointer
      • Pointer difference to calculate the distance between elements in an array
    • Using delete[] to release allocated memory
    • Implementing a destructor for the our_vector class to free dynamically allocated memory.
    • The "Rule of Three" : For our_vector , the destructor needs to be correctly defined along with a copy constructor and a copy assignment operator to prevent memory errors.
    • Copy Constructor, deep copy using new[] to allocate space for a copy of the array and copy the elements; deallocate with delete[]
    • Assignment operator, copy-and-swap idiom avoiding self-assignment
    • Prepend and Append Operations, insertion/deletion that require potentially expensive memory reallocation

    Pointer Arithmetic and Arrays

    • Pointer arithmetic involves adding and subtracting integers to/from pointers, altering memory addresses.
    • p + i (where p is a pointer and i is an integer) points to the ith element after the element pointed to by p.
    • Integer arithmetic is different from pointer arithmetic. Adding an integer to a pointer results in calculating a new address based on the size (in bytes) of the type being pointed to.
    • *(p + i) is used to access the element at the i-th position from the pointer p
    • Accessing the last element p[n] - note that p + n is one element past the last element.
    • Using the subscript operator [] which is equivalent to *(p + i).
    • Subtracting a number from a pointer, calculating the difference between pointers. A pointer difference (p₁ - p₂) calculates the distance in indexes of the elements pointed to by p₁ & p₂ (only valid if p1 and p2 point into the same array or refer to elements in consecutive memory locations).

    Iteration over an Array

    • Iterating using sequential pointer iteration (e.g., for (char* it = p; it != p + 3; ++it) , dereferencing and incrementing).
    • Index-based random access (e.g., for (int i = 0; i < 3; ++i)).

    Arrays in Functions

    • Passing arrays using pointers to the beginning and end of the array segment, e.g., begin and end, representing the first and one-past-the-last elements.
    • Using pointer notation with arrays: [begin, end).

    Array-Based Vector Class

    • Implementing a custom dynamic array class named our_vector, handling memory allocation and management, including dynamic resizing.
    • size() function returns the current size of the vector.
    • operator[] to support element access using array notation. This should be overloaded for both non-constant and constant vectors.
    • at(int i) often used for bounds checking.

    Memory Management with Dynamic Arrays

    • Vectors require dynamic memory management to grow/shrink
    • When inserting/deleting in the middle of the vector, other elements need to be shifted in memory (expensive operation).
    • To avoid frequent memory reallocation during insertion or deletion, vectors often allocate more memory than needed (resizing).
    • Important: When allocating memory with new[] , deallocate it with delete[] in the destructor to prevent memory leaks.

    Insert and Remove Elements

    • Implementing functions push_front, push_back, and remove for inserting and deleting elements. These potentially involve expensive memory reallocation due to contiguous memory layout.
    • These functions deal with memory reallocation for efficiency, given contiguous memory is in use.
    • Vector operations that change size are costly since contiguous memory is in use.

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    Related Documents

    Introduction to Computer Science PDF
    Dynamic Data Structures II Lecture Notes PDF
    Programmier-Befehle Woche 13 PDF

    Description

    Test your knowledge on dynamic data structures focusing on memory management and pointer arithmetic. This quiz covers the implementation of a vector class and the nuances of dynamic memory allocation using 'new'. Enhance your understanding of how vectors handle memory and pointers in C++.

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