2 - Dimensional array in C++

         This array is used to represent and store data in a tabular form. Such type of array specially used to represent data in a matrix form. It is an array having 2 subscript or indices.

Syntax

               storage class datatype arrayname[s1][s2];

Where ‘s1’ indicates number of rows and ‘s2’ indicates number of column.
      In C++ the subscript of the first array element is always zero. For instance, If a[5][5] is an array then the first element is always (by default) a[0][0].

Example

                int a[4][3];

                int x[m][n];

Where ‘m’ and ‘n’ are constant numbers.

Initialisation:- Like one dimensional array two dimensional array can be initialised with a list of values while declaring the array variable.

        Example

int a[3][2]={1,2,4,6,7,9};

         where

                a[0][0]=1                             a[0][1]=2

    a[1][0]=4                             a[1][1]=6

    a[2][0]=7                             a[2][1]=9

        alternate,

                int a[3][2]={{1,2},{4,6},{7,9}};

The row size is optional when array is initialised with a set of values.

Lets have an example.

Q. Write a program to read a matrix having m X n elements and display the sum of the main diagonal elements.

#include <iostream>

#include <stdlib.h>

void main()

{

   int a[10][10], m, n;

   cout<< “Enter row and column size ”;

   cin>>m>>n;

   if(m!=n)

   {

      cout<< “Diagonal elements don’t exist”;

      exit(1);

   }

   cout<< “Enter”<< m << “X” << n << “elements”;

   for(int i=0; i<m; i++)

      for(int j=0; j<n; j++)

         cin>>a[i][j];

   int s=0;

   for(int i=0; i<m; i++)

      for(int j=0; j<n; j++)

   if( i==j )

      s+=a[i][j];

   cout<< “Sum is ->”<<s;

} 




Q. Write a program to determine product of diagonal element of m X n matrix. 
Q. Write a program to determine sum and product of 2 matrices.