What is an Array in C?

An array is a fixed-size, contiguous collection of elements of the same data type stored sequentially in memory. In C, arrays provide index-based O(1) random access to elements.

Because array elements are stored in adjacent memory addresses, accessing arr[i] computes the memory offset as base_address + (i * sizeof(type)).

Declaring and Initializing 1D Arrays

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int main() {
    int scores[5] = {88, 92, 79, 95, 85};
    int length = 5;

    printf("Array elements:\n");
    for (int i = 0; i < length; i++) {
        printf("Element at index [%d] = %d (Address: %p)\n", i, scores[i], (void*)&scores[i]);
    }

    return 0;
}

Two-Dimensional (2D) Arrays & Matrices

2D arrays represent grids or matrices stored in row-major order in contiguous memory:

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int main() {
    int matrix[2][3] = {
        {10, 20, 30},
        {40, 50, 60}
    };

    printf("2D Array Grid:\n");
    for (int row = 0; row < 2; row++) {
        for (int col = 0; col < 3; col++) {
            printf("%d\t", matrix[row][col]);
        }
        printf("\n");
    }

    return 0;
}

Passing Arrays to Functions

When you pass an array to a function in C, it automatically decays into a pointer to its first element (int *arr or int arr[]). Therefore, you should always pass the array size as an additional argument:

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int calculateSum(int arr[], int size) {
    int total = 0;
    for (int i = 0; i < size; i++) {
        total += arr[i];
    }
    return total;
}

int main() {
    int values[] = {5, 10, 15, 20};
    int total = calculateSum(values, 4);

    printf("Total sum: %d\n", total);
    return 0;
}

Array Safety Guidelines

1. No Bounds Checking: C does not perform automatic runtime boundary checking. Accessing arr[10] in an array of size 5 results in undefined behavior or memory corruption.
2. Buffer Overflows: Always ensure iteration indices strictly satisfy 0 <= index < size.

Related Tutorials & Examples

• Learn structured composite data with Structures in C.
• Explore address arithmetic in the Pointers in C Guide.
• Practice multi-dimensional arrays with Matrix Multiplication in C and Bubble Sort in C.