C Arrays

Defination

In C, an array is a sequence of elements of the same type, arranged in adjacent memory slots and defined with a fixed length at compile time. Arrays serve as a structured means to handle multiple values under a single identifier, optimizing storage and access.

Declaration and Syntax

To create an array, specify the type, followed by the array name, and enclose the desired capacity in square brackets:

int scores[5];

Here, scores is a container for five integers, indexed from 0 to 4.

Storage and Memory Layout

Each element resides in sequential memory addresses, meaning the address of one item is directly followed by the next. This layout allows for efficient index-based access, but it also means the array size must be known ahead of time.

Initialization Techniques

Arrays can be populated during definition:

float values[3] = {3.5, 4.2, 5.1};

Alternatively, C permits partial initialization, filling remaining slots with default zero values:

char letters[4] = {'a', 'b'};

Uninitialized elements here become '\0'.

Accessing Components

You access individual elements by their position, beginning with index 0 as the first element.

printf("%d", scores[2]); // Access third item

Reading or updating is straightforward via this index mechanism.

Modifying Values

Changing the contents of an array item uses direct assignment:

scores[1] = 90;

This updates the second element to 90.

Multidimensional Arrays

For tabular data, C offers arrays of arrays (matrices):

int grid[2][3] = {     
      {1, 2, 3},     
      {4, 5, 6} 
}; 

You reference an item using multiple indices: grid[1][2] gives 6.

• Size rigidity: Array size is fixed upon creation.
• No boundary checks: C doesn't prevent out-of-bounds access.
• Cannot grow/shrink: Arrays are static—dynamic resizing requires pointers and memory management.

Passing Arrays to Functions

When arrays are sent to functions, they decay into pointers to the first element:

void display(int arr[], int length);

Within the function, you can iterate over the array using the given size.

Pointer Interactions

Arrays and pointers share a close relationship in C:

int *p = scores;

You can traverse the array with pointer arithmetic:

*(p + 1) = 75;

This assigns a value to the second item in the array using pointer arithmetic.

String as Character Arrays

Strings in C are implemented as null-terminated arrays of characters:

char word[] = "code";

This stores 'c', 'o', 'd', 'e', and '\0'.

Array of Pointers

Useful for string lists or dynamic memory scenarios:

char *cities[] = {"Paris", "Tokyo", "Delhi"};

Each item in this array holds the address of a string constant.

Quick Summary of C Arrays