Arrays

An array is a collection of elements of the same data type, stored in contiguous memory locations. Each element can be accessed directly using an index.

• Indexing starts from 0 in C.
• The size must be declared at creation time (fixed size).
• All elements are of the same type (e.g., all int or all float).

Memory Layout

If you declare:

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

then memory looks like this:

Each element can be accessed as arr[0], arr[1], etc.

When to Use Arrays

Use arrays when:

• The number of elements is known in advance and rarely changes.
• You need fast, random access to elements using an index.
• You are performing mathematical computations such as matrices or vectors.
• You need to store and process data sequentially, such as reading sensor values.

When Not to Use Arrays

Avoid arrays when:

• The size of data changes frequently (use a linked list instead).
• You need frequent insertions or deletions in the middle (shifting elements is costly).
• You need to store different data types (use structures).
• You are dealing with large data and need dynamic resizing (use dynamic arrays with malloc() or vectors in C++).

Example in C

#include <stdio.h>

int main() {
    int arr[5]; // Declare an array of 5 integers
    int i;

    // Input 5 numbers
    printf("Enter 5 numbers:\n");
    for (i = 0; i < 5; i++) {
        scanf("%d", &arr[i]);
    }

    // Display the numbers
    printf("\nYou entered:\n");
    for (i = 0; i < 5; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }

    // Example: Sum of all elements
    int sum = 0;
    for (i = 0; i < 5; i++) {
        sum += arr[i];
    }
    printf("\nSum = %d\n", sum);

    return 0;
}

Sample Output

Enter 5 numbers:
10 20 30 40 50

You entered:
arr[0] = 10
arr[1] = 20
arr[2] = 30
arr[3] = 40
arr[4] = 50

Sum = 150

Key Operations and Time Complexities

Advantages and Disadvantages