How to declare a 2D array dynamically in C++ using new operator

Prerequisite: Array Basics
In C/C++, multidimensional arrays in simple words as an array of arrays. Data in multidimensional arrays are stored in tabular form (in row major order). Below is the general form of declaring N-dimensional arrays:

:

data_type array_name[size1][size2]….[sizeN];

data_type: Type of data to be stored in the array. 
Here data_type is valid C/C++ data type
array_name: Name of the array
size1, size2, …, sizeN: Sizes of the dimensions

2D arrays are arrays of single-dimensional arrays.

:

data_type array_name[x][y];
data_type: Type of data to be stored. Valid C/C++ data type.

Below is the diagrammatic representation of 2D arrays:

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For more details on multidimensional and 2D arrays, please refer to Multidimensional arrays in C++ article.

Problem: Given a 2D array, the task is to dynamically allocate memory for a 2D array using new in C++.

Solution: Following 2D array is declared with 3 rows and 4 columns with the following values:

1 2 3 4
5 6 7 8
9 10 11 12

Note: Here M is the number of rows and N is the number of columns.

Method 1: using a single pointer - In this method, a memory block of size M*N is allocated and then the memory blocks are accessed using pointer arithmetic. Below is the program for the same:

1 2 3 4 
5 6 7 8 
9 10 11 12

Method 2: using an array of pointer: Here an array of pointers is created and then to each memory block. Below is the diagram to illustrate the concept:

👁 Image

Below is the program for the same: