Array Classification in Computer Programming with Declaration

Array in computer programming is used to store data items in a list, that may of any type. The array can be classified based on how the data items are arranged for human understanding. We have discussed about the concept of array, in this article we will classify an array.

The following figure shows the classification of the array:

Single dimensional arrays

A single dimensional array (also called one dimensional array) is a linear list consisting of related and similar data items. In memory, all the data items are stored in contiguous memory locations one after the other. Pictorial representation of single dimensional array is shown below:

Here, all the items are arranged in a row. It is called 'row major' arrangement. Instead, they can also be arranged column wise. It is called 'column major' arrangement. The memory requirement for the array depends on the type of data items stored and number of items. Let us assume, data items are of type int and assume that int takes 2 bytes (in majority of PCs size of integer will be 4 or 8 bytes). Since 5 elements are stored and the size of int is 2 bytes, the memory required for the array is 10 bytes. If the size of integer is 4 bytes, the array uses 40 bytes of memory and so on in general

Memory for array – n * sizeof (data type)

Where

• n  is the number of data items
• data type  the data type of data items

An array has the following basic properties:

• The data items (called elements) stored in the array should be of the same data type. The data items are stored contiguously in memory with subscript of the first item always 0 (zero).
• Each data item is accessed using the same name long with different subscript.
• The subscript or index of the array is always an integer.

Declaration of single dimensional arrays:

We know that all the variables are declared before they are used in the program. Similarly, an array must be declared before it is used. During declaration, the size of the array has to specify. The size used during declaration of the array informs the compiler to allocate and reserve the specified memory locations. A single dimensional array in C can be declared using the following syntax:

data_typearray_name[expression];

where

• data_type – can be a basic data type such as int, float, char, etc.
• array_name – is the name of the array
• expression – should be evaluated to a positive integer only. It can also be an integer constant. The expression should be enclosed within square brackets ‘[]’.

Note: Expression such as 10 or 10+2 is allowed. No variables are allowed in expression, for example, 10+b is not allowed because b is a variable.

For example, consider the following declaration statement: int arr[10];
The compiler reserves 10 locations (i.e. 2 *10 bytes) for the array arr. In each of the location we can store an integer value. The memory allocated by the compiler is, pictorially represented as: