Pointer arithmetic - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is pointer arithmetic in C?

Pointer arithmetic means adding or subtracting integers to or from pointers to move through memory locations of the data type the pointer points to.

beginner

How does adding 1 to a pointer affect its value?

Adding 1 to a pointer moves it to the next element of its type in memory. For example, if it points to an int, it moves forward by sizeof(int) bytes.

intermediate

What happens when you subtract two pointers?

Subtracting two pointers gives the number of elements between them, not the byte difference. Both pointers must point to elements of the same array.

beginner

Why can't you add two pointers together?

Adding two pointers is not allowed because it doesn't make sense to combine two memory addresses. Pointer arithmetic only supports adding or subtracting integers to pointers.

intermediate

Explain how pointer arithmetic relates to array indexing.

Array indexing like arr[i] is actually pointer arithmetic under the hood. It means *(arr + i), moving the pointer i elements forward and accessing that value.

If p is an int* pointing to address 1000 and sizeof(int) is 4, what is the address of p + 2?

A 1002

B 1008

C 1004

D 1006

Adding 2 to p moves it 2 elements forward. Each int is 4 bytes, so 2 * 4 = 8 bytes. 1000 + 8 = 1008.

What does the expression (p2 - p1) return if p1 and p2 are pointers to elements in the same array?

A The byte difference between p2 and p1

B The sum of the addresses

C An error

D The number of elements between p1 and p2

Subtracting pointers returns how many elements apart they are, not the byte difference.

Which of these operations is NOT valid in pointer arithmetic?

A p1 + p2

B p - 1

C p1 - p2

D p + 3

You cannot add two pointers together. Only add or subtract integers to/from pointers.

What does arr[i] mean in terms of pointers?

A arr - i

B arr + i

C *(arr + i)

D *(i + arr - 1)

Array indexing is pointer arithmetic: arr[i] is the same as *(arr + i).

If p points to a char and p = p + 5, how many bytes does p move forward?

A 5 bytes

B 1 byte

C Depends on the system

D 10 bytes

A char is 1 byte, so moving 5 elements forward moves 5 bytes.

Describe what happens when you add an integer to a pointer in C.

Think about how arrays and pointers relate.

Explain why subtracting two pointers gives the number of elements between them, not the byte difference.

Consider how pointer arithmetic is designed for array navigation.