Programming Techniques DT143G - Lecture 9: Pointers
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Questions and Answers

What is the main purpose of using pointers in programming?

  • To prevent the modification of variable values.
  • To facilitate the creation of dynamic arrays. (correct)
  • To simplify data structures by hiding them.
  • To allocate fixed memory sizes.

    • How is a pointer declared in C?

  • type *name; (correct)
  • pointer type name;
  • type name;
  • name* type;

    • What does the expression &a represent in C?

  • The number of elements in a.
  • The value stored in variable a.
  • The address of the variable a. (correct)
  • The pointer pointing to variable a.

    • What happens when a pointer points to an incorrect memory location?

    <p>A segmentation fault may occur.</p> Signup and view all the answers

    In the swap function example, what is the purpose of using pointers?

    <p>To change the values of variables directly.</p> Signup and view all the answers

    What is a characteristic of dynamic arrays compared to static arrays?

    <p>Dynamic arrays can change size during program execution.</p> Signup and view all the answers

    Which statement about pointers is NOT true?

    <p>Pointers must always refer to distinct variables.</p> Signup and view all the answers

    Why is it necessary to have a dedicated space in memory when using pointers?

    <p>To modify variables accurately.</p> Signup and view all the answers

    Study Notes

    Programmeringsteknik DT143G - Lecture 9: Pointers and Dynamic Arrays

    • Lecture: Pointers and Dynamic Arrays
    • Date: 3-12-2024
    • Lecturer: Pascal Rebreyend

    Today's Contents

    • Pointers - definition
    • Using Pointers with Functions
    • Dynamic Arrays
    • Memory Allocations

    Why Pointers?

    • Essential for dynamic arrays in C
    • Convenient and efficient for irregular data structures
    • Found in other languages, but often hidden or named differently
    • Needed to understand many algorithms and data structures (future courses)

    Definition and Usage

    • Pointers: Variables that hold memory addresses
    • Declaration: type *name; (e.g., int *ptr;)
    • Address-of Operator: &a gives the address of variable a
    • Dereference Operator: *p gives the value at address p
      • behaves like other standard data types.

    Example 1: Modification via a Function

    • Demonstrates using pointers to modify variables inside a function (swap function example provided).
    • Showed changing values of given variables in a different function.
    • swap Function example with pointers.

    Comments

    • & Operator in scanf: Explained how to use & in the function
    • Side Effects: Pointers can lead to unexpected behavior if not managed correctly.
    • Memory Errors: Incorrect pointer usage can cause segmentation faults or incorrect values.
    • Important: Pointers store memory addresses, not the data itself

    Memory Allocation

    • malloc(size_t s): Allocates s bytes of memory and returns a pointer to the allocated space.
    • calloc(size_t nb, size_t size): Allocates memory for an array of nb elements, each of size size bytes. Returns a pointer to the allocated memory.
    • free(void* ptr): Releases the memory block pointed to by ptr.
    • sizeof(type): Returns the size (in bytes) of a data type.

    Example: Dynamic Arrays

    • Demonstrates allocating and using dynamic arrays in C using calloc.
    • Shows fill_array and print_array examples with dynamic arrays.

    Comments (Dynamic Arrays)

    • Memory Leaks: Critical to free allocated memory to prevent memory leaks.
    • Multidimensional Arrays: Different ways to represent multidimensional arrays using pointers.
    • Index Protection: Be mindful of array bounds when using dynamic arrays; array indexing must be calculated properly to avoid segmentation faults.

    Conclusion

    • Pointers: Fundamental in C (key concept)
    • Variable Modification: Pointers enable modifying variables within functions.
    • Dynamic Arrays: Efficiently manage arrays with variable sizes at run time
    • Simplicity, Power, Risk: Pointers offer simplicity and flexibility but can be risky if not handled carefully.

    Optional - Later

    • Pointers to Functions: Pointers can hold the addresses of functions which is especially useful with functions like qsort.
    • realloc and reallocarray: Allows modifying the size of dynamically allocated memory if needed.

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    L9_Pointers1 PDF - Programmeringsteknik DT143G Lecture Notes

    Description

    This quiz covers Lecture 9 of the DT143G Programming Techniques course, focusing on the concept of pointers and dynamic arrays. Students will explore the definition and usage of pointers, memory allocations, and their significance in programming, particularly in C. Prepare to test your understanding of these critical programming concepts.

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