Array in C language

 

Array in C Language

Arrays are one of the most important and frequently used data structures in the C programming language. They allow us to store multiple values of the same data type in a single variable. Understanding arrays is essential for mastering C because they form the foundation for advanced topics like strings, pointers, structures, and dynamic memory allocation.

1. Introduction to Arrays

An array is a collection of elements of the same data type stored in contiguous memory locations. Instead of declaring many variables separately, we can use an array to store similar values.

Example without array:

int a1 = 10;
int a2 = 20;
int a3 = 30;

Example with array:

int a[3] = {10, 20, 30};

Here:

  • a is the array name.
  • 3 is the size.
  • Elements are accessed using index numbers (starting from 0).

2. Declaration of Array

Syntax:

data_type array_name[size];

Example:

int marks[5];

This declares an array named marks that can store 5 integers.

3. Initialization of Array

Arrays can be initialized at the time of declaration.

Method 1: Full Initialization

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

Method 2: Partial Initialization

int arr[5] = {1, 2};

Remaining elements become 0.

Method 3: Without Size

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

Compiler automatically counts the size (3).

4. Accessing Array Elements

Array elements are accessed using index numbers.

  • Index starts from 0
  • Last index = size - 1
int arr[3] = {10, 20, 30};

printf("%d", arr[0]);  // Output: 10
printf("%d", arr[2]);  // Output: 30

5. Memory Representation of Array

Arrays store elements in contiguous memory locations.

If:

int arr[3] = {10, 20, 30};

Memory layout (assuming 4 bytes per int):

Index Value Address Example
0 10 1000
1 20 1004
2 30 1008

Formula:

Address = Base Address + (Index × Size of Data Type)

6. Input and Output in Array

Taking Input:

int arr[5];
for(int i = 0; i < 5; i++) {
    scanf("%d", &arr[i]);
}

Printing Output:

for(int i = 0; i < 5; i++) {
    printf("%d ", arr[i]);
}

7. Types of Arrays in C

1. One-Dimensional Array

Simple linear array.

int arr[5];

2. Two-Dimensional Array

Used for matrices (rows and columns).

int matrix[3][3];

Accessing:

matrix[0][1];

Initialization:

int matrix[2][2] = {
    {1, 2},
    {3, 4}
};

3. Multi-Dimensional Array

More than two dimensions.

int arr[2][3][4];

8. Strings as Arrays

In C, strings are arrays of characters ending with a null character \0.

char name[6] = "Hello";

Memory: H e l l o \0

Example:

printf("%s", name);

9. Passing Array to Function

Arrays are passed by reference (actually by address).

void display(int arr[], int size) {
    for(int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
}

int main() {
    int arr[3] = {1, 2, 3};
    display(arr, 3);
}

Important:

  • Changes inside function affect original array.

10. Array and Pointers

Array name represents the base address.

int arr[3] = {10, 20, 30};

arr is equivalent to &arr[0].

Pointer example:

int *ptr = arr;
printf("%d", *(ptr + 1));  // Output: 20

Relationship:

arr[i] == *(arr + i)

11. Dynamic Array in C

Static arrays have fixed size. For flexible size, use dynamic memory allocation.

Using malloc():

#include <stdlib.h>

int *arr;
arr = (int*) malloc(5 * sizeof(int));

Free memory:

free(arr);

12. Common Array Operations

1. Traversing

Accessing all elements.

2. Searching

Linear Search:

for(int i = 0; i < n; i++) {
    if(arr[i] == key)
        printf("Found");
}

Binary Search (Sorted Array Required)

3. Sorting

Bubble Sort Example:

for(int i = 0; i < n-1; i++) {
    for(int j = 0; j < n-i-1; j++) {
        if(arr[j] > arr[j+1]) {
            int temp = arr[j];
            arr[j] = arr[j+1];
            arr[j+1] = temp;
        }
    }
}

13. Advantages of Arrays

  1. Easy to store multiple values.
  2. Random access using index.
  3. Efficient memory usage.
  4. Useful for implementing other data structures like stacks, queues.

14. Disadvantages of Arrays

  1. Fixed size (in static arrays).
  2. Insertion and deletion are costly.
  3. Cannot store different data types.
  4. Risk of out-of-bounds error.

15. Applications of Arrays

  1. Storing marks of students.
  2. Matrix operations.
  3. String handling.
  4. Searching and sorting algorithms.
  5. Implementing stacks and queues.
  6. Image processing.
  7. Statistical calculations.

16. Important Concepts Related to Arrays

1. Array Index Out of Bounds

Accessing invalid index causes undefined behavior.

int arr[3];
arr[5] = 10;  // Dangerous

2. Array Size Determination

int size = sizeof(arr) / sizeof(arr[0]);

3. Const Array

const int arr[3] = {1,2,3};

Values cannot be changed.

17. Difference Between Array and Pointer

Array Pointer
Fixed memory Dynamic memory
Size fixed Can change location
arr++ not allowed ptr++ allowed

18. Example Program (Complete)

#include <stdio.h>

int main() {
    int n, sum = 0;

    printf("Enter number of elements: ");
    scanf("%d", &n);

    int arr[n];

    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        sum += arr[i];
    }

    printf("Sum = %d", sum);

    return 0;
}

19. Multidimensional Array Memory Formula

For 2D array:

Address = Base + [(Row × Total Columns) + Column] × Size

Conclusion

Arrays are a fundamental concept in C programming. They provide a structured way to store and manipulate multiple data elements efficiently. Understanding array declaration, initialization, memory representation, pointer relationship, and operations like searching and sorting is essential for mastering C.

Comments

Post a Comment

Popular Posts