Array Manipulation

What is an Array?

An array in C is a contiguous block of memory that stores multiple elements of the same data type. It allows you to:

• Group variables together under a single name
• Access each item using an index
• Efficiently perform operations like iteration, sum, reverse, etc.

Core Array Syntax and Usage in C

Array Declaration

int numbers[10];        // Array of 10 integers
uint8_t buffer[32];     // 32-byte buffer (commonly used in firmware)
Declares a fixed-size array — memory is allocated statically.

Array Initialization

int values[4] = {10, 20, 30, 40};     // full initialization
int empty[4] = {0};                   // all elements = 0
char message[] = "Hi";                // string-style init

If you skip the size (like message[ ]) , the compiler counts the size automatically.

Accessing Array Elements

int arr[3] = {5, 10, 15};
printf("%d", arr[1]);     // prints 10
arr[2] = 20;               // modify element at index 2

The index starts from 0. Always ensure you stay within 0 to n-1.

Array Size with sizeof()

int arr[5];
int total_bytes = sizeof(arr);        // e.g., 20 if int = 4 bytes
int element_bytes = sizeof(arr[0]);  // gives size of int i.e. 4 bytes 
int element_count = sizeof(arr) / sizeof(arr[0]);  // gives 5

This only works within the same scope where the array is declared (not when passed to a function).

Memory Layout (Example)

int arr[4] = {10, 20, 30, 40};

Assuming the starting address is 0x2000, the memory looks like:

Each int = 4 bytes (on most systems).

Where Arrays Are Used in Firmware

In embedded systems, arrays are used for:

• Data buffers (UART, SPI, ADC)
• Sensor samples
• Circular queues
• Protocol packets/frames
• Bitmaps/lookup tables

Relevance in Embedded

• Arrays = lightweight, deterministic memory structures
• You work without dynamic memory, so statically allocated arrays are essential
• Used in interrupt routines, communication, and data processing
   

Common Pitfalls (Practical Tips)

• Off-by-one errors: If n = 5, then valid indices are 0 to 4 (not 5).
• Wrong type for storage: If you’re reading bytes, use uint8_t[] not int[].
• Forgetting to initialize: Especially in statically defined buffers.
• Overwriting data in fixed-size buffers — always check bounds.
• Mixing pointers and arrays incorrectly — be clear whether you’re passing array base or pointer offset.