What is an Array in C Programming?

In C Programming, an array can be defined as number of memory locations, each of which can store the same data type and which can be references through the same variable name.

An array defined in a very straightforward syntax in C as below:

An array is a collective name given to a group of similar quantities or values. These similar quantities could be percentage marks of 100 students, number of chairs in home, or salaries of 300 employees or ages of 25 students. Thus an array is a collection of similar elements. These similar elements could be all integers or all floats or all characters etc. Usually, the array of characters is called a “string”, where as an array of integers or floats is called simply an array. All elements of any given array must be of the same type i.e we can’t have an array of 10 numbers, of which 5 are int and 5 are float.

 

Arrays and pointers have a special relationship as arrays use pointers to reference memory locations.



How to declare an Array in C?

Arrays should be declared before they can be used in the C program. Standard array declaration is as

Here data_type specifies the variable type of the element which is going to be stored in the array. In C programming language we can declare the array of any basic standard types. For example

Here we declared array height of double data type and size 10, array width of float data type and size 20, array min of int data type and size 9, array name of char data type and size 5.

How to view and access Array elements?

In C programming, array elements are accessed with indices which starts at position 0. The elements of the array occupy adjacent locations in memory. C treats the name of the array as if it were a pointer to the first element. This is important in understanding how to do arithmetic with arrays. Any item in the array can be accessed through its index, and it can be accessed any where from with in the program. So

Here, variable m will have the value of first item of array height.

The following C program will declare an array of five integers and prints all the elements of the array.

How to initialize arrays in C Programming?

In C, arrays can be initialized in two ways 1) initializing while declaration 2) initializing after declamation. The initializing values are enclosed within the curly braces in the declaration.

Here is an example which declares and initializes an array of five elements of type int. Array can also be initialized after declaration. Look at the following C code which demonstrate the declaration and  initialization of an array.

Initializing array while declaration

int age[5] = {19, 10, 8, 17, 9};

int age[] = {19, 10, 8, 17, 9};

Initializing array after declaration

Initializing and printing arrays by using for loops

Here is a C program that will demonstrate how we can use for loop to initialize arrays.

The output of the above C program is as below:

How to perform operations on arrays in C?

Here is a more complex program that demonstrates how to read, write and traverse integer arrays in C programming. There is also another source code to compare two arrays in C.

How to copy one array into another?

There is no such statement in C language which can directly copy an array into another array. So we have to copy each item separately into another array.

To summarize, arrays are provides a simple mechanism where more than one elements of same type are to be used. We can maintain, manipulate and store multiple elements of same type in one array variable and access them through index.

Multidimensional Arrays in C

In C programming you can have arrays of any dimensions. To understand the concept of multidimensional arrays let us consider the following 4 X 5 matrix

Row number (i) Column numbers (j)
0 11 3 5 -9 -6
1 5 6 -8 7 24
2 -8 9 2 12 45
3 10 13 -10 4 5

Let us assume the name of matrix is x

To access a particular element from the array we have to use two subscripts on for row number and other for column number the notation is of the form X [i] [j] where i stands for row subscripts and j stands for column subscripts. Thus X [0] [0] refers to 10, X [2] [1] refers to 16 and so on In short multidimensional arrays are defined more or less in the same manner as single dimensional arrays, except that for subscripts you require two squire two square brackets. We will restrict our decision to two dimensional arrays.

Below given are some typical two-dimensional array definitions

The first example defines tables as a floating point array having 50 rows and 50 columns. The total number of elements in this array are 2500 (50 x 50).

The second declaration example establishes an array line of type character with 24 rows and 40 columns. The number of elements is 1620 (24 X 40).

Consider the following two dimensional array definition

int values [3] [4] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. 11, 12 };

Here the first subscript stands for the row number and second one for column number. First subscript ranges from 0 to 2 and there are altogether 3 rows second one ranges from 0 to 3 and there are altogether 4 columns.

Alternatively the above definition can be defined and initialized as

Here the values in first pair of braces are initialized to elements of first row, the values of second pair of inner braces are assigned to second row and so on. Note that outer pair of curly braces is required. If there are two few values within a pair of braces the remaining elements will be assigned as zeros.

Here is a sample program that stores roll numbers and marks obtained by a student side by side in matrix

The above example illustrates how a two dimensional array can be read and how the values stored in the array can be displayed on screen.