Data Structures

Data Structures – Array

What is an Array?

An array is collection of items stored at contiguous memory locations. The idea is to store multiple items of same type(Homogeneous) together. This makes it easier to calculate the position of each element by simply adding an offset to a base value, i.e., the memory location of the first element of the array (generally denoted by the name of the array).

What is Contiguous Memory?

  • Contiguous memory allocation is a classical memory allocation model that assigns a process consecutive memory blocks (that is, memory blocks having consecutive addresses).
  • Contiguous memory allocation is one of the oldest memory allocation schemes. When a process needs to execute, memory is requested by the process. The size of the process is compared with the amount of contiguous main memory available to execute the process. If sufficient contiguous memory is found, the process is allocated memory to start its execution. Otherwise, it is added to a queue of waiting processes until sufficient free contiguous memory is available.

Types of indexing in array:

  • 0 (zero-based indexing): The first element of the array is indexed by subscript of 0
  • 1 (one-based indexing): The first element of the array is indexed by subscript of 1
  • n (n-based indexing): The base index of an array can be freely chosen. Usually programming languages allowing n-based indexing also allow negative index values and other scalar data types like enumerations, or characters may be used as an array index.


  • It is better and convenient way of storing the data of same datatype with same size.
  • In Arrays, the elements can be accessed randomly by using the index number.
  • It allocates memory in contiguous memory locations for its elements. It does not allocate any extra space/ memory for its elements. Hence there is no memory overflow or shortage of memory in arrays.
  • Iterating the arrays using their index is faster compared to any other methods like linked list etc.
  • It allows to store the elements in any dimensional array – supports multidimensional array.
  • Using Arrays, other data structures like Linked List, Stacks, Queues, etc., can be implemented.


  • It allows us to enter only fixed number of elements into it. We cannot alter the size of the array once array is declared. Hence if we need to insert more number of records than declared then it is not possible. We should know array size at the compile time itself.
  • Inserting and deleting the records from the array would be costly since we add / delete the elements from the array, we need to manage memory space too.
  • It does not verify the indexes while compiling the array. In case there is any indexes pointed which is more than the dimension specified, then we will get run time errors rather than identifying them at compile time.
    • Array indexes always begin with 0. Hence when we say array of size 10, array has elements from index 0 to 9. If we specify or use array as intArr[10], intArr[11], intArr[200], the C compiler will not show any error, but we will get run time errors while executing the program.


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