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# C++ Multi-dimensional Arrays

C++ allows multidimensional arrays. Here is the general form of a multidimensional array declaration:

    type name[size1][size2]...[sizeN];

For example, the following declaration creates a three dimensional 5 . 10 . 4 integer array:

    int threedim[5][10][4];

# Two-Dimensional Arrays:

The simplest form of the multidimensional array is the two-dimensional array. A two-dimensional array is, in essence, a list of one-dimensional arrays. To declare a two-dimensional integer array of size x,y you would write something as follows:

    type arrayName [ x ][ y ];

Where type can be any valid C++ data type and arrayName will be a valid C++ identifier.

A two dimensional array can be think as a table which will have x number of rows and y number of columns. A 2-dimentional array a which contains three rows and four columns can be shown as below:

Thus, every element in array a is identified by an element name of the form a[ i ][ j ], where a is the name of the array, and i and j are the subscripts that uniquely identify each element in a.

# Initializing Two-Dimensional Arrays:

Multidimensioned arrays may be initialized by specifying bracketed values for each row. Following is an array with 3 rows and each row have 4 columns.

    int a[3][4] = {
     {0, 1, 2, 3} ,   /*  initializers for row indexed by 0 */
     {4, 5, 6, 7} ,   /*  initializers for row indexed by 1 */
     {8, 9, 10, 11}   /*  initializers for row indexed by 2 */
    };

The nested braces, which indicate the intended row, are optional. The following initialization is equivalent to previous example:

    int a[3][4] = {0,1,2,3,4,5,6,7,8,9,10,11};

# Accessing Two-Dimensional Array Elements:

An element in 2-dimensional array is accessed by using the subscripts ie. row index and column index of the array. For example:

    int val = a[2][3];

The above statement will take 4th element from the 3rd row of the array. You can verify it in the above digram.

    #include <iostream>
    using namespace std;

    int main ()
    {
       // an array with 5 rows and 2 columns.
       int a[5][2] = { {0,0}, {1,2}, {2,4}, {3,6},{4,8}};

       // output each array element's value
       for ( int i = 0; i < 5; i++ )
          for ( int j = 0; j < 2; j++ )
          {
             cout << "a[" << i << "][" << j << "]: ";
             cout << a[i][j]<< endl;
          }

       return 0;
    }

When the above code is compiled and executed, it produces following result:

    a[0][0]: 0
    a[0][1]: 0
    a[1][0]: 1
    a[1][1]: 2
    a[2][0]: 2
    a[2][1]: 4
    a[3][0]: 3
    a[3][1]: 6
    a[4][0]: 4
    a[4][1]: 8

As explained above, you can have arrays with any number of dimensions, although it is likely that most of the arrays you create will be of one or two dimensions.

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