Welcome to the ninth part of the Gentle Introduction to C series. As said before this series aims to provide you a brief introduction to C language.

In this post, we will learn about a very basic data structure, namely single-dimensional array, often just called array.

Interesting Fact : Array is at the base of computer memory. Computer memory is just a very big array.

Array

Array is a collection of similar objects or items which are stored in a contiguous fashion.

Let us understand this definition by breaking it into two parts.

Collection of Similar Items

Array can be used to store almost any data type. However given the data type, we cannot store data items of any other kind in it.

Example :

Sample Valid Array

The above array is valid and is an example of an int type array.

Sample Invalid Array

However, the above array is invalid because the array contains more than one type, namely char, float and int.

Stored in Contiguous Manner

Array elements, in the computer memory, are stored in contiguous memory locations. Hence by knowing the memory address of any of the elements of an array, we can reach to any other array element by just traversing the memory addresses in a linear fashion.


Note : Array elements in C (and most of the programming languages) can be accessed using their index. Indexes are like placeholder which can be used to get information or value at any position in the array. In C, 0-based indexing is used i.e. the first element is at the 0th index position.

Example :

Indexing in Array

Declaring an Array

An array in C can be declared in three different ways.

  1. Declaration by Specifying Size
    datatype arr_name[size];
  2. Declaration by Initialising Array
    datatype arr_name[]={items, in, a, comma, seperated, list};
  3. Declaration by Specifying Size and Initialising Array
    datatype arr_name[size]={size, items, in, a, comma, seperated, list};

For example,

int a[10];
char name[]={'a', 'a', 'y', 'u', 's', 'h'};
char foo[6]={'r', 'a', 'n', 'd', 'o','m'};

In the above code snippet, three arrays have been declared one, a, of int type of size 10 and the others, name and foo, of char type and size 6.


Note : An array declaration like,

char bar[1]={'m', 'o', 'h', 'a', 'n'};

will not give a compiler error and rather will just give a warning. However this declaration is not encouraged.


Accessing Array Elements

As said above, array elements can be accessed using indexes. In C (and many similar programming languages), indexes start at 0 and are always positive.

To access the nth element in an array arr_name we will write the array name followed by the index in square brackets i.e.

arr_name[n-1]

For example, in the above given array name, if we want to access the first char, we can do so by

name[0];

Note :

arr[-1];
arr[100];

In C, there is no index out of bound checking i.e. if for a given array, arr of size 10, the above code snippet will not give any error, however the results returned will be unexpected and totally garbage.


Array is a data structure that is not only limited to C and rather is fundamental to almost all programming languages. There are some flaws in array, particularly it's static nature, which are overcame in many other array-like data structures. However array is often the starting point for many applications.

There is still much to be said about arrays, in particular of it's other variant i.e. multi-dimensional array but I will leave that for another post.

Thanks for reading.