Arrays in C

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

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1. One-Dimensional Arrays

Declaration:

data_type array_name[size];
int marks[5];

Initialisation:

int marks[5] = {85, 90, 78, 92, 88};
int zeros[5] = {0};            /* all elements 0 */
int arr[] = {1, 2, 3, 4, 5};  /* size inferred */

Accessing elements:

marks[0] = 85;   /* first element (index 0) */
marks[4] = 88;   /* last element (index 4) */

Traversal:

#include <stdio.h>

int main() {
    int arr[5] = {10, 20, 30, 40, 50};
    for (int i = 0; i < 5; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }
    return 0;
}

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2. Two-Dimensional Arrays (Matrices)

Declaration:

int matrix[3][3];

Initialisation:

int matrix[2][3] = {
    {1, 2, 3},
    {4, 5, 6}
};

Matrix addition example:

int a[2][2] = {{1,2},{3,4}};
int b[2][2] = {{5,6},{7,8}};
int c[2][2];

for (int i = 0; i < 2; i++)
    for (int j = 0; j < 2; j++)
        c[i][j] = a[i][j] + b[i][j];

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3. String as Character Array

char name[20] = "Alice";
char greeting[] = {'H','e','l','l','o','\0'};  /* null-terminated */

Common string functions (string.h):

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Passing Arrays to Functions

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

int main() {
    int data[] = {5, 10, 15, 20};
    printArray(data, 4);
    return 0;
}

Note: Arrays are always passed by reference — the function receives a pointer to the first element.