C++: Two-dimensional array

Two-dimensional array

Two-dimensional (2D) arrays are collection of similar elements where the elements are stored in certain number of rows and columns. An example m × n matrix where m denotes the number of rows and n denotes the number of columns is shown in Figure12.4

int arr[3][3];

Declaration of 2-D array

The declaration of a 2-D array is

data-type array_name[row-size][col-size];

In the above declaration, data-type refers to any valid C++ data-type, array_name refers to the name of the 2-D array, row-size refers to the number of rows and col-size refers to the number of columns in the 2-D array.

For example

int A[3][4];

In the above example, A is a 2-D array, 3 denotes the number of rows and 4 denotes the number of columns. This array can hold a maximum of 12 elements.

Array size must be an unsigned integer value which is greater than 0. In arrays, column size is compulsory but row size is optional.

Other examples of 2-D array are:

int A[3][3];

float x[2][3];

char name[5][20];

Initialization of Two-Dimensional array

The array can be initialized in more than one way at the time of 2-D array declaration. For example

int matrix[4][3]={

{10,20,30},// Initializes row 0

{40,50,60},// Initializes row 1

{70,80,90},// Initializes row 2

{100,110,120}// Initializes row 3

};

int matrix[4][3]={10,20,30,40,50,60,70,80,90,100,110,120};

Array’s row size is optional but column size is compulsory.

For example

int matrix[][3]={

{10,20,30},// row 0

{40,50,60},// row 1

{70,80,90},// row 2

{100,110,120}// row 3

};

Accessing the two-dimensional array

Two-dimensional array uses two index values to access a particular element in it, where the first index specifies the row value and second index specifies the column value.

matrix[0][0]=10;// Assign 10 to the first element of the first row

matrix[0][1]=20;// Assign 20 to the second element of the first row

matrix[1][2]=60;// Assign 60 to the third element of the second row

matrix[3][0]=100;// Assign 100 to the first element of the fourth row

Write a program to perform addition of two matrices

#include<iostream>

#include<conio>

using namespace std;

int main()

{

      int row, col, m1[10][10], m2[10][10], sum[10][10];

      cout<<"Enter the number of rows : ";

      cin>>row;

      cout<<"Enter the number of columns : ";

      cin>>col;

      cout<< "Enter the elements of first matrix: "<<endl;

      for (int i = 0;i<row;i++ )

      for (int j = 0;j <col;j++ )

      cin>>m1[i][j];

      cout<< "Enter the elements of second matrix: "<<endl;

      for (int i = 0;i<row;i++ )

      for (int j = 0;j<col;j++ )

      cin>>m2[i][j];

      cout<<"Output: "<<endl;

      for (int i = 0;i<row;i++ )

      for (int j = 0;j<col;j++ )

      {

      sum[i][j]=m1[i][j]+m2[i][j];

      cout<<sum[i][j]<<" ";

      }

      cout<<endl<<endl;

      }

getch();

return 0;

}

Memory representation of 2-D array

Normally, the two-dimensional array can be viewed as a matrix. The conceptual view of a 2-D array is shown below:

int A[4][3];

In the above example, the 2-D array name A has 4 rows and 3 columns.

Like one-dimensional, the 2-D array elements are stored in continuous memory.

There are two types of 2-D array memory representations. They are:

• Row-Major order

• Column-Major order

For example

int A[4][3]={

{ 8,6,5}, { 2,1,9}, {3,6,4}, {4,3,2},

Row Major order

In row-major order, all the elements are stored row by row in continuous memory locations, that is, all the elements in first row, then in the second row and so on. The memory representation of row major order is as shown below;

Column Major order