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ARRAY in C Language - Declaration & Initialization


Array is the collection of similar data types or collection of similar entity stored in contiguous memory location. Array of character is a string. Each data item of an array is called an element. And each element is unique and located in separated memory location. Each of elements of an array share a variable but each element having different index no. known as subscript. 

An array can be a single dimensional or multi-dimensional and number of subscripts determines its dimension. And number of subscript is always starts with zero. One dimensional array is known as vector and two dimensional arrays are known as matrix. 

 ADVANTAGES: array variable can store more than one value at a time where other variable can store one value at a time.


int arr[100];

int mark[100]; 


     Its syntax is : 

     Data type array name [size]; 

             int arr[100]; 

             int mark[100]; 

                int a[5]={10,20,30,100,5} 

The declaration of an array tells the compiler that, the data type, name of the array, size of the array and for each element it occupies memory space. Like for int data type, it occupies 2 bytes for each element and for float it occupies 4 byte for each element etc. The size of the array operates the number of elements that can be stored in an array and it may be a int constant or constant int expression. 

We can represent individual array as : 

         int ar[5]; 

         ar[0], ar[1], ar[2], ar[3], ar[4]; 

Symbolic constant can also be used to specify the size of the array as: 

         #define SIZE 10;


After declaration element of local array has garbage value. If it is global or static array then it will be automatically initialize with zero. An explicitly it can be initialize that 

         Data type array name [size] = {value1, value2, value3…} 


         int ar[5]={20,60,90, 100,120} 

Array subscript always start from zero which is known as lower bound and upper value is known as upper bound and the last subscript value is one less than the size of array. Subscript can be an expression i.e. integer value. It can be any integer, integer constant, integer variable, integer expression or return value from functional call that yield integer value. 

So if i & j are not variable then the valid subscript are 

         ar [i*7],ar[i*i],ar[i++],ar[3]; 

The array elements are standing in continuous memory locations and the amount of storage required for hold the element depend in its size & type.

Total size in byte for 1D array is: 

     Total bytes=size of (data type) * size of array. 

     Example : if an array declared is: 

             int [20]; 

             Total byte= 2 * 20 =40 byte. 


/*Write a program to input values into an array and display them*/ 


int main() 

        int arr[5],i; 

        for(i=0;i<5;i++) { 

            printf(“enter a value for arr[%d] \n”,i); 



        printf(“the array elements are: \n”); 

        for (i=0;i<5;i++) 




    return 0; 


Enter a value for arr[0] = 12

Enter a value for arr[1] =45 

Enter a value for arr[2] =59 

Enter a value for arr[3] =98 

Enter a value for arr[4] =21 

The array elements are 12 45 59 98 21 

Two dimensional arrays 

Two dimensional array is known as matrix. The array declaration in both the array single dimensional array single subscript is used and in two dimensional array two subscripts are is used. 

Its syntax is 

Data-type array name[row][column]; 

Or we can say 2-d array is a collection of 1-D array placed one below the other.

Total no. of elements in 2-D array is calculated as row*column 


         int a[2][3]; 

         Total no of elements=row*column is 2*3 =6 

It means the matrix consist of 2 rows and 3 columns 

For example:- 

 20 2 7 

 8 3 15 

Initialization of 2-d array: 

2-D array can be initialized in a way similar to that of 1-D array. for example:- int mat[4][3]={11,12,13,14,15,16,17,18,19,20,21,22};


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