Two Dimensional Arrays in C++

May 19, 2025

Introduction to Two Dimensional Arrays in C++

When working with data like grids, tables, or matrices in C++, two-dimensional arrays in C++(2D arrays) become incredibly useful. They allow you to store data in a structured format using rows and columns, just like a spreadsheet. This blog will describe you through everything you need to know about 2D arrays in C++, from basic initialization to performing operations like matrix addition.

The 2D array is organized as matrices which can be represented as the collection of rows and columns.

Two Dimensional Array in C++ for arranging in row and column

What is Two Dimensional Arrays in C++?

A two-dimensional array in C++ is an array of arrays. In simple words, it’s a way to store data in rows and columns format. It’s perfect when you need to represent a table, matrix, or grid.

  • The elements of 2D arrays can be randomly accessed. Similar to one-dimensional arrays, we can access the individual cells in a 2D array by using the indices of the cells.
  • There are two indices attached to a particular cell, one is its row number while the other is its column number.

Syntax : 

The syntax of declaring a two-dimensional array is very much similar to that of a one-dimensional array, given as follows.

datatype arrayName[rows][columns];

Example:

int marks[3][4];
Two Dimensional Arrays In C++
Two Dimensional Arrays In C++
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Introduction to Arrays

Sorting of Array

Array Rotation

Reverse an array or string

Find pairs in array with given sum

How to Initialize a 2D Array

Size of 2-D array

The total number of elements that can be stored in a multidimensional array can be calculated by multiplying the size of all the dimensions.

Example: The array int a[5][6] can store total (5*6) = 30 elements.

Initializing 2D Arrays

  • DIRECT METHOD

    data_type[ ][ ] variable_name = { {R1C1, R1C2, ….}, {R2C1,R2C2, ….} };

    Example: int [ ][ ] arr = { { 2 ,  4 } ,  {6, 8 } };

  • USING LOOPS

    We can use loops for initializing 2d array like
    for (int i = 0; i < 2; i++)
  {
    for (int j = 0; j < 2; j++)
      {
	int a = x[i][j];
      }
  }

You can fill in the values of a 2D array either at the time of declaration or later during program execution. To initialize a 2D Array, we mainly use three different way –

1. Full Initialization

2. Partial Initialization

3. Inline Initialization

1. Full Initialization

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

This creates a 2-row and 3-column array.

2. Partial Initialization

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

Here, the missing values will be automatically filled with 0.

3. Inline Initialization

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

You can skip the row size if column size is mentioned.

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How to Print a 2D Array in C++

To print all elements of a 2D array, we use nested loops – one loop for rows and another for columns.

Example:

for (int i = 0; i < 2; i++) {
for (int j = 0; j < 3; j++) {
cout << matrix[i][j] << " ";
}
cout << endl;
}

This will display the 2D array in matrix form.

How to Take 2D Array Input from User

We can ask the user to enter elements of the array using cin.

Example: Taking 3×3 matrix input

int arr[3][3];
cout << "Enter elements of 3x3 matrix: " << endl;

for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
cin >> arr[i][j];
}
}

This helps the program accept dynamic input from users instead of fixed values.

Matrix Addition using Two Dimensional Array in C++

Matrix addition is a common operation where you add corresponding elements of two matrices.

Example:

int A[2][2] = {{1, 2}, {3, 4}};
int B[2][2] = {{5, 6}, {7, 8}};
int result[2][2];

for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
result[i][j] = A[i][j] + B[i][j];
}
}

Output:

6 8
10 12

Pointer to a 2D Array in C++

You can also use pointers to access a 2D array. This helps in memory-level access and efficient programming.

Example:

int arr[2][2] = {{1, 2}, {3, 4}};
int (*ptr)[2] = arr;

cout << *(*(ptr + 1) + 1); // Output: 4

Here, ptr points to the first row, and pointer arithmetic helps access any element in the array.

Passing 2D Array to a Function in C++

To use a 2D array inside a function (for display, calculation, etc.), you must pass it properly with the number of columns mentioned.

Example:

void display(int arr[][3], int rows) {
for (int i = 0; i < rows; i++) {
for (int j = 0; j < 3; j++) {
cout << arr[i][j] << " ";
}
cout << endl;
}
}

Calling the Function:

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

Conclusion

A two-dimensional array in C++ is a powerful way to organize data in rows and columns. Whether you’re working with student marks, matrices, or tables – 2D arrays make the job easier. By learning how to initialize, input, print, and pass them to functions, you are building the foundation for more complex applications like image processing, game development, and scientific computing.

FAQs

Static 2D arrays allocate memory contiguously in row-major order, where rows are stored sequentially. Dynamic 2D arrays (using pointers or new) may involve non-contiguous memory blocks, as each row is allocated separately. This affects pointer arithmetic and cache performance during traversal.

Three common approaches include specifying the column size explicitly (e.g., void func(int arr[], int rows)), using a pointer to an array (e.g., void func(int (*arr), int rows)), or passing a double pointer for dynamically allocated arrays (e.g., void func(int** arr, int rows, int cols)). The column size must be known for static arrays to ensure correct memory offset calculations.

Use nested new and delete[] operations:

int** arr = new int*[rows]; 
for(int i=0; i<rows; i++) 
arr[i] = new int[cols]; 
// Deallocation 
for(int i=0; i<rows; i++) 
delete[] arr[i]; 
delete[] arr;

Failing to deallocate any tier of memory causes leaks

Due to cache locality, row-major order favors row-wise traversal. For example:

for(int i=0; i<rows; i++) 
for(int j=0; j<cols; j++) 
arr[i][j];

Column-wise traversal jumps across memory blocks, leading to cache misses and slower execution.

Common pitfalls include incorrect initialization (e.g., mismatched row sizes in braces), out-of-bounds access, assuming dynamic arrays are contiguous, and type mismatches when passing arrays to functions. For example, treating int[][] as int** without proper casting can cause runtime errors.

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  • Tree Traversals: Depth First Search (DFS) : C | C++ | Java
  • Construct a Binary Tree from Postorder and Inorder

B – Trees

AVL Trees

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