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 represents the total number of elements it can hold. For example, int arr[5]; means the array can store 5 integers.

beginner

What happens if you try to 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 size of a statically declared array in C++?

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

beginner

Why is it important to stay within array bounds when accessing elements?

Staying within bounds prevents errors and crashes. It ensures you only access valid memory locations, keeping your program safe and stable.

intermediate

What is the difference between array size and array bounds?

Array size is how many elements the array can hold. Array bounds are the valid index range, usually from 0 to size-1. Accessing outside bounds is unsafe.

If you declare int arr[10];, what is the highest valid index you can use?

A 10

B 11

C 0

D 9

Array indices start at 0, so the highest valid index is size - 1, which is 9.

What does sizeof(arr) return for int arr[5]; if an int is 4 bytes?

A 5

B 20

C 4

D 1

sizeof(arr) returns total bytes. 5 elements × 4 bytes = 20 bytes.

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

A Undefined behavior

B Compile error

C Always zero

D Valid access

Index 10 is outside bounds (0-9), so accessing it causes undefined behavior.

How can you safely find the number of elements in a static array?

A Use <code>sizeof(arr) / sizeof(arr[0])</code>

B Use <code>arr.length()</code>

C Use <code>arr.size()</code>

D Use <code>count(arr)</code>

Only sizeof(arr) / sizeof(arr[0]) works for static arrays in C++.

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

A It causes syntax errors

B It wastes memory

C It leads to undefined behavior and possible crashes

D It slows down the program

Accessing out-of-bounds elements can cause unpredictable program behavior or crashes.

Explain what array size and array bounds mean in C++ and why they matter.

Think about how many elements an array can hold and which indexes are safe to use.

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

Remember sizeof(arr) gives total bytes, and sizeof(arr[0]) gives bytes per element.