Data Structures

Question 1

What does the function realloc do?

Answer 1

Allocates a requested amount of memory on the heap and returns an address to the start of the reserved memory.

Question 2

What happens when you realloc
a variable old_ptr that is null?

Answer 2

Realloc will work like malloc

Question 3

What happens when you realloc
a variable old_ptr that is NOT null?

Answer 3

If old_ptr is not null, will allocate enough memory for the new length using malloc and copy the old from old_ptr to new memory and then will free old_ptr.

Question 4

How do you define a multi-dimensional array? (e.g 2d int array)

Answer 4

int days[2][13] = {
{0, 31, 28, 31, 30, 31, 30,
31, 31, 30, 31, 30, 31},
{0, 31, 29, 31, 30, 31, 30,
31, 31, 30, 31, 30, 31}
};

days[1][2];

Question 5

What is an alternative approach of storing a multidimensional array?

Answer 5

Using pointer arrays.

Question 6

How is memory allocated for multi-dimensional dynamic arrays?

Answer 6

With the use of an additional array containing pointers. Each array is not necessarily stored contiguously in memory.

Question 7

What is the advantage of storing arrays in memory with one pointer?

Answer 7

• Simpler with memory management
• All allocated in heap memory in one go
  -Each array is stored contiguously

Question 8

What is the disadvantage of storing arrays in memory with one pointer?

Answer 8

If using big data, a large free contiguous block of memory to be free is required.

Question 9

What are the advantages of storing arrays contiguously?

Answer 9

• When accessing consecutively, we can be efficient with memory access
• Allows for pointer arithmetic

Question 10

What is a struct?

Answer 10

Data structure/Mechanism for packing multiple variables into a single block.

Question 11

How do structs differ to objects?

Answer 11

Structs don’t have functions.

Question 12

How can we access member variables of struct data structure?

Answer 12

Dot-syntax to access remember variables.

Question 13

What are the advantages of struct?

Answer 13

• Helps keep correlated variables together
• Logical ordering and structure to data representation
• Pass multiple variables packed together as a single parameter to a function
• A struct allows you to return multiple variables from a function
• A struct can embed structs within it.

Question 14

What is arrow syntax equivalent to?

Answer 14

• dereferencing a point, and
• accessing a member variables
  at the same time.

Question 15

What will the sizeof(struct x) give at compile time?

Answer 15

Gives the byte size of the variables.

Question 16

What are unions in C?

Answer 16

Unions in C are a data container that can be defined to store a single item of one or more types. An instance of a union can only contain one item at any time but you can predefine all possible types of the item stored inside a union.

Question 17

What types can be stored in a union?

Answer 17

Any existing type (including a struct or union)

Question 18

What is the size of a union?

Answer 18

The size of the biggest type within the union.