Array size and bounds in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the size of an array represent in C?

The size of an array in C represents the total number of elements it can hold. For example, int arr[5]; means the array can hold 5 integers.

beginner

What happens if you access an array element outside its bounds in C?

Accessing an element outside the array bounds leads to undefined behavior. This means the program might crash, show wrong data, or behave unpredictably.

intermediate

How do you find the number of elements in an array in C?

You can find the number of elements by dividing the total size of the array by the size of one element: sizeof(arr) / sizeof(arr[0]).

beginner

Why is it important to stay within array bounds?

Staying within array bounds prevents bugs and crashes. It ensures your program accesses only valid memory, keeping data safe and the program stable.

beginner

What is the index range for an array declared as int arr[10];?

The valid index range is from 0 to 9. Arrays in C start at index 0, so the last element is at index size-1.

If you declare char letters[4];, what is the highest valid index you can use?

A 3

B 4

C 5

D 0

Array indices start at 0, so for 4 elements, valid indices are 0, 1, 2, and 3.

What does sizeof(arr) / sizeof(arr[0]) calculate for an array arr?

A Memory address of the array

B Size of one element

C Total bytes used by the array

D Number of elements in the array

Dividing total size by element size gives the number of elements.

What is the result of accessing arr[10] if int arr[10]; is declared?

A Last element of the array

B Undefined behavior

C Value 0

D Compile-time error

Accessing outside the array bounds causes undefined behavior, not a compile error.

Which of these is a valid array declaration for 5 integers?

A int arr();

B int arr;

C int arr[5];

D int arr{};

Only int arr[5]; declares an array of 5 integers.

Why should you avoid accessing array elements beyond their declared size?

A To prevent program crashes and data corruption

B To make the program run faster

C To save memory

D To increase array size automatically

Accessing out of bounds can cause crashes or corrupt data.

Explain what array bounds mean and why they are important in C programming.

Think about how arrays store data and what happens if you try to use invalid positions.

Describe how to calculate the number of elements in a C array using the sizeof operator.

Remember sizeof gives size in bytes.