Multidimensional Arrays

The C language allows arrays of any type including arrays of arrays. These are sometimes known as multidimensional arrays.

For Example:

double x[10][20];

is a declaration for an array, x, with 10   elements, each of which contains an array with   20 elements.

Declarations of arrays	Notes
int a[100];	a one-dimensional array
int b[4][8];	a two-dimensional array
int c[5][3][2];	a three-dimensional array

In the preceding example, each element of the array is accessed using the expression

x[ i ][ j ]

The Array indices can not be  folded into one subscript in c language,

 x[ i , j ]

2D or Two Dimensional Array

Visualizes a 2D array as a matrix that has both rows and columns

For example, an array declared as

int a[3][4];

the array elements are arranged as follows:

	Column0	Column1	Column2	Column3
row0	a [0][0]	a[0][1]	a[0][2]	a[0][3]
row1	a[1][0]	a[1][1]	a[1][2]	a[1][3]
row2	a[2][0]	a[2][1]	a[2][2]	a[2][3]

The general form of a 2D array declaration is:

e_type a_name[r_size][c_size];

where

• e_type is the type of the array elements
• a_name is the name of the array
• r_size is the number of rows in the array
• c_size is the number of columns in the array

The number of pairs of brackets, [ ], denotes the dimensionality.

2D Array Initialization

• An array initializer is a sequence of initializing values written as a brace-enclosed, comma-separated list.
• Each row is contained in braces.
• Each element in a two-dimensional array is referenced using an identifier followed by two subscripts [ ] [ ]
• The subscript values for both rows and columns begin with 0, and each subscript has its own set of brackets.

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

declares j to be a 2´2, 4-element, integer array whose elements have the initial values

j[0][0]=1 j[0][1]=2
j[1][0]=3 j[1][1]=4

The following three array initializations are equivalent.

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

Higher Dimensional Arrays

C allows arrays to be defined with more than two subscripts. A three-dimensional (3D) array is really a series of two-dimensional arrays. For example, to declare a 3D array volume:

int volume[10][10][10];

Declares a 10´10´10 array containing 1000 elements: essentially 10 2D arrays, each containing 100 elements.

3D arrays are often used to specify 3D information.

4D arrays are often used to specify time-series data.