Lecture 11: Arrays and Multi-dimensional Arrays in C

🎯 Learning Objectives

                    By the end of this lecture, you will be able to:
                    Understand the concept and need for arrays in programming
Declare, initialize, and access elements of one-dimensional arrays
Perform operations on arrays (input, output, searching, sorting)
Understand multi-dimensional arrays, especially 2D arrays
Work with matrices using 2D arrays
Apply array concepts to solve real-world problems

                

📊 What is an Array?

An array is a collection of elements of the same data type, stored in contiguous memory locations and accessed using a common name and index.

Key Characteristics:

Homogeneous: All elements must be of the same data type
Indexed: Elements are accessed using indices (starting from 0)
Fixed Size: Size is determined at declaration time
Contiguous Memory: Elements are stored in consecutive memory locations

Real-world Example: Think of an array like a row of lockers in a school - each locker has a number (index) and can store items of the same type.

🔧 Array Declaration and Initialization

Syntax: data_type array_name[size];

Declaration Examples:

int numbers[5];        // Array of 5 integers
float grades[10];      // Array of 10 floating-point numbers
char name[20];         // Array of 20 characters (string)

Initialization Methods:

// Method 1: Initialize during declaration
int arr1[5] = {10, 20, 30, 40, 50};

// Method 2: Partial initialization (remaining elements = 0)
int arr2[5] = {10, 20};  // {10, 20, 0, 0, 0}

// Method 3: Size determined by initializer
int arr3[] = {1, 2, 3, 4, 5};  // Size = 5

// Method 4: Initialize all elements to 0
int arr4[5] = {0};

💾 Array Memory Representation

Let's visualize how array

int arr[5] = {10, 20, 30, 40, 50}

is stored in memory:

10

arr[0]

20

arr[1]

30

arr[2]

40

arr[3]

50

arr[4]

Important: Array indices start from 0. For an array of size n, valid indices are 0 to n-1.

Memory Address Calculation:

If base address = 1000 and each integer takes 4 bytes:

arr[0] → 1000
arr[1] → 1004
arr[2] → 1008
arr[3] → 1012
arr[4] → 1016

⚡ Basic Array Operations

1. Input and Output:

#include <stdio.h>

int main() {
    int arr[5];
    int i;
    
    // Input elements
    printf("Enter 5 integers: ");
    for(i = 0; i < 5; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Output elements
    printf("Array elements: ");
    for(i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    
    return 0;
}

2. Finding Maximum Element:

int findMax(int arr[], int size) {
    int max = arr[0];
    for(int i = 1; i < size; i++) {
        if(arr[i] > max) {
            max = arr[i];
        }
    }
    return max;
}

🔢 Multi-dimensional Arrays

A multi-dimensional array is an array of arrays. The most common is the 2D array, which can be thought of as a table with rows and columns.

2D Array Declaration:

data_type array_name[rows][columns];

// Examples of 2D array declaration
int matrix[3][4];        // 3 rows, 4 columns
float grades[5][3];      // 5 students, 3 subjects
char board[3][3];        // 3x3 tic-tac-toe board

2D Array Initialization:

            // Method 1: Row-wise initialization
int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};

// Method 2: Linear initialization
int matrix[2][3] = {1, 2, 3, 4, 5, 6};

// Method 3: Partial initialization
int matrix[2][3] = {{1, 2}, {4}};  // Remaining elements = 0

🎨 2D Array Visualization

Let's visualize a 2D array: int matrix[3][4] = {{1,2,3,4}, {5,6,7,8}, {9,10,11,12}}

1

2

3

4

5

6

7

8

9

10

11

12

Accessing Elements:

matrix[0][0] = 1 (first row, first column)
matrix[1][2] = 7 (second row, third column)
matrix[2][3] = 12 (third row, fourth column)

Remember: Both row and column indices start from 0!

🔄 2D Array Operations

1. Input and Output:

#include <stdio.h>

int main() {
    int matrix[3][3];
    int i, j;
    
    // Input elements
    printf("Enter elements of 3x3 matrix:\n");
    for(i = 0; i < 3; i++) {
        for(j = 0; j < 3; j++) {
            printf("Enter element [%d][%d]: ", i, j);
            scanf("%d", &matrix[i][j]);
        }
    }
    
    // Output elements
    printf("\nMatrix:\n");
    for(i = 0; i < 3; i++) {
        for(j = 0; j < 3; j++) {
            printf("%d\t", matrix[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

➕ Matrix Operations

Matrix Addition:

   
// Function to add two matrices
void addMatrices(int a[][3], int b[][3], int result[][3], int rows, int cols) {
    for(int i = 0; i < rows; i++) {
        for(int j = 0; j < cols; j++) {
            result[i][j] = a[i][j] + b[i][j];
        }
    }
}

Matrix Multiplication:

// Function to multiply two matrices
void multiplyMatrices(int a[][3], int b[][3], int result[][3], int r1, int c1, int c2) {
    for(int i = 0; i < r1; i++) {
        for(int j = 0; j < c2; j++) {
            result[i][j] = 0;
            for(int k = 0; k < c1; k++) {
                result[i][j] += a[i][k] * b[k][j];
            }
        }
}
}

Note: For matrix multiplication A×B, the number of columns in A must equal the number of rows in B.

🌟 Practical Applications

Arrays are used in:

Student Management: Storing grades, roll numbers
Image Processing: 2D arrays represent pixel values
Game Development: Game boards, maps, inventories
Mathematical Computing: Vectors, matrices, statistics
Data Analysis: Storing and processing large datasets

Real Example: Student Grade Management

// 2D array: 5 students, 3 subjects
float grades[5][3] = {
    {85.5, 92.0, 78.5},  // Student 1
    {90.0, 87.5, 95.0},  // Student 2
    {78.0, 82.5, 88.0},  // Student 3
    {92.5, 89.0, 91.5},  // Student 4
    {87.0, 85.5, 90.0}   // Student 5
};

// Calculate average for each student
for(int i = 0; i < 5; i++) {
    float sum = 0;
    for(int j = 0; j < 3; j++) {
        sum += grades[i][j];
    }
    printf("Student %d average: %.2f\n", i+1, sum/3);
}

⚠️ Common Pitfalls & Best Practices

Common Mistakes:

Array Bounds: Accessing arr[5] in an array of size 5
Uninitialized Arrays: Using array elements without initialization
Wrong Index: Starting loops from 1 instead of 0
Size Confusion: Forgetting array size in function parameters

Best Practices:

Always initialize arrays before use
Use meaningful variable names
Check array bounds in loops
Use constants for array sizes
Document your array usage

// Good practice: Use constants
#define MAX_STUDENTS 50
#define MAX_SUBJECTS 5

int grades[MAX_STUDENTS][MAX_SUBJECTS];

// Good practice: Bounds checking
if(index >= 0 && index < MAX_STUDENTS) {
    // Safe to access grades[index]
}

📋 Summary

                    Key Concepts Covered:
                    Arrays: Collections of similar data types
Indexing: Zero-based indexing for element access
1D Arrays: Linear collections with single dimension
2D Arrays: Matrix-like structures with rows and columns
Operations: Input/output, searching, mathematical operations
Applications: Data management, mathematical computing, games

                

Next Lecture Preview:

Lecture 12: Functions in C Programming

Function declaration and definition
Parameter passing (call by value, call by reference)
Arrays as function parameters
Recursive functions

Thank you for your attention! 🎓

Questions and discussions are welcome!

Arrays and Multi-dimensional Arrays

Unit III: Array and Function | Lecture 11

🎯 Learning Objectives

By the end of this lecture, you will be able to:

📊 What is an Array?

Key Characteristics:

🔧 Array Declaration and Initialization

Declaration Examples:

Initialization Methods:

💾 Array Memory Representation

Memory Address Calculation:

⚡ Basic Array Operations

1. Input and Output:

2. Finding Maximum Element:

🔢 Multi-dimensional Arrays

2D Array Declaration:

2D Array Initialization:

🎨 2D Array Visualization

Accessing Elements:

🔄 2D Array Operations

1. Input and Output:

➕ Matrix Operations

Matrix Addition:

Matrix Multiplication:

🌟 Practical Applications

Arrays are used in:

Real Example: Student Grade Management

⚠️ Common Pitfalls & Best Practices

Common Mistakes:

Best Practices:

📋 Summary

Key Concepts Covered:

Next Lecture Preview:

Thank you for your attention! 🎓