C Arrays

1D Arrays

An array is a collection of elements of the same data type stored in contiguous memory locations. Array indices start at 0.

// Declaration
int numbers[5];

// Declaration with initialization
int numbers[5] = {10, 20, 30, 40, 50};

// Size inferred from initializer
int numbers[] = {10, 20, 30, 40, 50};

// Access element
printf("%d", numbers[0]);  // 10
numbers[2] = 99;           // modify element

2D Arrays (Matrices)

A 2D array is an array of arrays — essentially a matrix with rows and columns.

// Declaration: rows x columns
int matrix[3][4];

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

// Access: matrix[row][col]
printf("%d", matrix[1][2]);  // 6

1D Array — Declare, Initialize, Traverse

#include <stdio.h>

int main() {
    int scores[] = {85, 92, 78, 95, 88};
    int n = sizeof(scores) / sizeof(scores[0]);  // number of elements = 5

    // Traverse and print
    printf("Scores: ");
    for (int i = 0; i < n; i++) {
        printf("%d ", scores[i]);
    }
    printf("\n");

    // Find sum and average
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum += scores[i];
    }
    printf("Sum: %d\n", sum);
    printf("Average: %.2f\n", (float)sum / n);

    // Find maximum
    int max = scores[0];
    for (int i = 1; i < n; i++) {
        if (scores[i] > max) max = scores[i];
    }
    printf("Max: %d\n", max);

    return 0;
}

/*
Scores: 85 92 78 95 88
Sum: 438
Average: 87.60
Max: 95
*/

2D Array — Matrix Addition

#include <stdio.h>

int main() {
    int a[2][3] = {{1, 2, 3}, {4, 5, 6}};
    int b[2][3] = {{7, 8, 9}, {10, 11, 12}};
    int c[2][3];

    // Matrix addition
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            c[i][j] = a[i][j] + b[i][j];
        }
    }

    // Print result matrix
    printf("Matrix A + B:\n");
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%4d", c[i][j]);
        }
        printf("\n");
    }

    return 0;
}

/*
Matrix A + B:
   8  10  12
  14  16  18
*/

Passing Array to Function — Find Max Element

#include <stdio.h>

// Arrays are always passed by reference (pointer to first 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;
}

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

// Passing 2D array to function
void print2D(int rows, int cols, int arr[rows][cols]) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%4d", arr[i][j]);
        }
        printf("\n");
    }
}

int main() {
    int nums[] = {34, 12, 67, 45, 89, 23};
    int n = sizeof(nums) / sizeof(nums[0]);

    printf("Array: ");
    printArray(nums, n);
    printf("Max element: %d\n", findMax(nums, n));

    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
    printf("\n2D Array:\n");
    print2D(2, 3, matrix);

    return 0;
}

/*
Array: 34 12 67 45 89 23
Max element: 89

2D Array:
   1   2   3
   4   5   6
*/

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C Arrays

1D Arrays

2D Arrays (Matrices)

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