Unit-3: Arrays in Computer Science

Unit-3: Arrays

• Arrays are a structured data type used to store multiple data items with common characteristics.
• Mathematically, arrays are denoted using indexed form (e.g., x₁, x₂, x₃, ..., xₙ).
• Arrays are essential in various applications, including reading numbers from input, sorting data, and calculating statistical measures (like mode and standard deviation).

Examples of Arrays

• Real-world examples include a list of books, a table of student grades, or a set of leaves arranged in a circular pattern.
• Arrays can be visualized as collections of data items arranged in a linear or multi-dimensional structure.

Basic Concept

• Arrays in computer science allow storing and manipulating ordered collections of data.
• Essential for multiple data items of similar characteristics.

1-D, 2-D, and 3-D Arrays

• 1-D array: A single row (list).
• 2-D array: A table (matrix - rows & columns).
• 3-D array: A cube-like structure (rows, columns, and depth).

Introduction to Arrays

• Arrays are structured collections of homogenous data (same type).
• Stored in contiguous memory locations.
• The number of subscripts represents dimensions of the array (e.g., a single subscript for 1-D, two subscripts for 2-D).

Defining an Array

• Array definition resembles variable declaration, but includes a size specification (e.g., integer constant representing number of elements in a 1D array).
• General syntax: storage-class data-type arrayname[expression];

Defining an Array - Example

• Using initialization: int marks[6] = {89, 90, 76, 78, 98, 86};
• Array index starts at 0. The size of an array cannot change after definition.

Length of an Array

• Length of array = Upper Limit - Lower Limit + 1
• Example for int marks[8]: Length is 8; upper limit is 7, lower limit is 0

Array Bounds in C

• In C, there's no automatic bound checking. Accessing an element out of array bounds can lead to program errors, not caught during the compile.

Basic Array Initialization

• Initializing arrays: int marks[5] = {72, 83, 65, 80, 76};
• If the supplied values are fewer than the array's allocated space, the remaining elements are set to zero for numeric types, and indeterminate for char types.

Initialization with Subscript

• Elements can be explicitly initialized while declaring, i.e int matrix[4][3] = {[0][0]=1, [1][1]=5, [2][2]=9};

Accessing Array Elements

• Elements are accessed using array_name[index].

How an Array is Stored in Memory

• Successive array elements are stored sequentially in memory.
• The starting address (x) and number of bytes per element (k) determines the memory location of any element a[i].

String Arrays

• Strings are arrays of characters that end with null character \0.
• Characters are stored in memory in ASCII format (e.g."Hello").
• Strings are initialized within double quotes: char str[] = "hello";

String functions

• strcpy: Copies the contents of one string to another
• strlen: Calculates and returns the length of the string.
• strcmp: Compares two strings; returns 0 if identical, non-zero otherwise
• strcat: Concatenates (joins) two strings.

2-D Arrays

• 2-D arrays are used to store tabular data.
• Arrays are declared as type arrayName[rowSize][colSize];
• Example: int marks[4][5];

2-D Arrays access

• Elements are accessed using two indices arrayName[row][col];

2-D Arrays Storage

• Elements are stored row by row in memory.

Multi-Dimensional Arrays (Beyond 2-D)

• C supports arrays of three or more dimensions.
• Declared as type arrayName[size1][size2]...[sizeN];

Passing Arrays to Functions

• Array names in function calls represent the starting address of the array.
• When an array is passed to a function It's passed by reference, any changes made within the called function will affect original array's content.
• Arrays passed by value would only pass the address to the function. Copying array contents is not done.

Enumerated Data Types

• Enumerated data type declares a named set of constants (e.g.: colors = {red, blue, green}).
• Values are assigned automatically, starting from 0. Can be explicitly defined.

Explore the fundamental concepts of arrays in computer science. This quiz covers 1-D, 2-D, and 3-D arrays, their structure, and real-world applications. Enhance your understanding of how arrays are used for organizing and manipulating data effectively.