Lecture 3 - Pointers, Arrays, Strings and Dynamic Memory Allocation

Question 1

What is a pointer in C?

Answer 1

A pointer is a variable that stores the memory address of another variable. It is declared using the * symbol.

int *ptr;

Question 2

How do you declare a pointer to an integer in C?

Answer 2

int *ptr;

This declares ptr as a pointer to an int.

Question 3

How do you get the address of a variable in C?

Answer 3

The address of a variable can be obtained using the & operator.

int x = 10;
int *ptr = &x;

Question 4

How do you dereference a pointer in C?

Answer 4

Dereferencing a pointer is done using the * operator to access the value stored at the memory address.

int x = 10;
int *ptr = &x;
int y = *ptr;  // y gets the value 10

Question 5

What is pointer arithmetic in C?

Answer 5

Pointer arithmetic allows you to increment or decrement pointers. When you increment a pointer, it moves by the size of the data type it points to.

int arr[5] = {1, 2, 3, 4, 5};
int *ptr = arr;
ptr++;  // Now points to the second element

Question 6

How is an array different from a pointer in C?

Answer 6

An array is a fixed-size sequence of elements, whereas a pointer can point to any memory location. However, the name of an array acts like a pointer to the first element.

Question 7

What is the relationship between arrays and pointers in C?

Answer 7

The name of an array is a pointer to its first element. For example, if arr is an array, arr is equivalent to &arr[0].

Question 8

How do you declare and initialize an array in C?

Answer 8

int arr[5] = {1, 2, 3, 4, 5};

Question 9

What is a string in C?

Answer 9

A string in C is an array of characters terminated by a null character '\0'. Strings are stored as char[] or char*.

Question 10

How do you declare and initialize a string in C?

Answer 10

char str[] = "Hello, World!";

This creates a string with the value "Hello, World!" and an implicit null terminator '\0'.

Question 11

What is malloc and how is it used in C?

Answer 11

malloc is used to dynamically allocate memory at runtime. It returns a pointer to the allocated memory.

int *arr = (int*)malloc(5 * sizeof(int));

Question 12

How do you access individual characters in a string?

Answer 12

Strings are arrays of characters, so you can access individual characters using array notation.

char str[] = "Hello";
char first_char = str[0];  // 'H'

Question 13

What is free and why is it used?

Answer 13

free is used to release memory that was previously allocated using malloc, calloc, or realloc.

free(arr);

Question 13

What is calloc and how is it different from malloc?

Answer 13

calloc allocates memory for an array of elements and initializes all the bytes to zero. Unlike malloc, it takes two arguments (number of elements and size of each element).

int *arr = (int*)calloc(5, sizeof(int));

Question 14

What is the purpose of realloc in C?

Answer 14

realloc is used to resize a previously allocated memory block.

arr = (int*)realloc(arr, 10 * sizeof(int));

Question 15

How do you pass an array to a function in C?

Answer 15

Arrays are always passed by reference (as pointers) to functions.

void printArray(int arr[], int size);

Question 16

What is a multi-dimensional array in C?

Answer 16

A multi-dimensional array is an array of arrays. For example, a two-dimensional array can be declared as:

int arr[3][4];

Question 17

How do you dynamically allocate a 2D array in C?

Answer 17

A 2D array can be dynamically allocated by using a pointer to a pointer and malloc or calloc.

int **arr = (int**)malloc(rows * sizeof(int*));
for (int i = 0; i < rows; i++) {
    arr[i] = (int*)malloc(cols * sizeof(int));
}

Question 18

What are the default initialization values for arrays in C?

Answer 18

Global arrays: Initialized to zero.
Local arrays: Contain garbage values unless explicitly initialized.

Question 19

How can you create a dynamically allocated string in C?

Answer 19

You can use malloc or calloc to allocate memory for a string dynamically.

char *str = (char*)malloc(20 * sizeof(char));