Array In C

Array is a term used for the collection of similar data type elements.

An array is a secondary data type derived from fundamental.It must have data type int, char, double float, struct or union but every element under an array identifier must have the similar data type.

Example

Suppose we required 5 integer elements in a program then there are two ways to allocate memory:

— Declare 5 different variables to store data.

int val1=10;

int val2=20;

int val3=30;

int val4=40;

int val5=50;

— Declare an array to store 5 values under a single variable name.

1	int arr_num[5]={10,20,30,40,50};

Array Declaration

Syntax

datatype array_Variable_Name[Max_Element_Count];

Example

— Declare an array of 5 integer datatype elements.

1	int arr_num[5];

Pronounce above declaration as “arr_num is an array of 5 integer datatype elements”.

int = array elements data type

arr_num= array variable or identifier

[5]=number of elements

— Declare An array of 5 character datatype elements

1	char arr_var[5];

Pronounce above declaration as “arr_var is an array of 5 character type elements”.

char = array elements data type

arr_var= array variable or identifier

[5]=number of elements

— Declare An array of 5 decimal datatype elements

1	float arr_var[5];

Pronounce above declaration as “arr_var is an array of 5 float or decimal datatype elements”.

float= array elements data type

arr_var= array variable or identifier

[5]=number of elements

Declare An array of structure for 5 employee information.

struct employee

{

unsigned char name[20];

unsigned long int empId;

double salary;

}emp[5];

Pronounce above declaration as “emp is an array of 5 employee type structure”.

struct employee = data type

emp= structure variable/identifier

[5]=number of elements

Array Initialization

A declared array may have some garbage data at the allocated memory location. So to be on safe side it is best practice to initialize the array with zero value at the time of declaration.

Syntax

datatype array_Variable_Name[Max_Element_Count]={val1,val2,val3,…….valn};
OR
datatype array_Variable_Name[ ]={val1,val2,val3,…….valn};

In Syntax 1 Number of elements in the array cannot exceed beyond the declared Max_Element_Count so

array size = Max_Element_Count*sizeof(dataType).

In Syntax 2 Number of elements in the array is not fixed so the size of the array will be-

array size=number of initialized array elements*sizeof(dataType).

Example

— Initialize an array of 5 integer datatype elements with value 10,20,30,40,50.

int arr_num[5]={10,20,30,40,50};

int arr_num[]={10,20,30,40,50};

— Declare An array of 5 character datatype elements.

1	char arr_var[5]={'A','M','I','T'};

— Declare An array of 5 decimal datatype elements.

1	float arr_var[5]={4.34,6.88,1.00,5};

— Declare An array of structure for 5 employee information.

struct employee

{

unsigned char name[20];

unsigned long int empId;

double salary;

}emp[5]={"Amit",32767,75000.67,"Mayank",56544,54567.564};

Points to remember for Array initialization

— Array Index always starts from 0.

— In the array, all the indexes are present at the continuous memory location.

#include<stdio.h>

int main()

{

char name[5]={'A','m','i','t'};

int i;

for(i=0;i<5;i++)

{

printf("Address of %dth index = %p\n",i,&name[i]);/*%p is use for Address print in Hex format*/

}

return 0;

}

Address of 0th index = 0x7ffd2696d6e0

Address of 1th index = 0x7ffd2696d6e1

Address of 2th index = 0x7ffd2696d6e2

Address of 3th index = 0x7ffd2696d6e3

Address of 4th index = 0x7ffd2696d6e4

You can see the difference between the continuous addresses is 1 byte because the array is char data type and char data type size is 1 byte, for int and float it will be 4 bytes because of their memory size.

— If the number of initialized array element < Max_Element_Count of an array then rest of the uninitialized Indexes will automatically initialize to zero.

1	int arr_num[5]={10,20};

— The number of initialized array element must be less than the declared array size.

#include<stdio.h>

int main()

{

int arr[5]={10,20,30,40,50,60,10,20,30,40,50};

int i;

for(i=0;i<10;i++)

{

printf("%d, ",arr[i]);

}

return 0;

}

When compiling this program, compiler will execute program with following warning-

warning:

excess elements in array initializer

int arr[5]={10,20,30,40,50,60,10,20,30,40,50};

Output:

10, 20, 30, 40, 50, 32766, 2114791168, -221224951, 4195872, 0,

See the output.Data is correct till 5 elements and after that, some garbage values received because array reserved memory only for 5 elements.

Note: Sometimes it causes segmentation fault also.

Size of array is equal to Max_Element_Count*sizeof(dataType).

#include<stdio.h>

int main()

{

int arr[5]={10,20,30};

printf("Size of array is =%ld",sizeof(arr));/*size of arr=size*sizeof(int)=5*4=20*/

return 0;

}

Output:

Size of array is =20

So you can understand Array size calculation like this –

size of arr = size*sizeof(int) = 5 X 4 = 20

Array In C

Array In C

Example

Array Declaration

Syntax

Example

— Declare an array of 5 integer datatype elements.

— Declare An array of 5 character datatype elements

— Declare An array of 5 decimal datatype elements

Declare An array of structure for 5 employee information.

Array Initialization

Syntax

Example

Points to remember for Array initialization

— Array Index always starts from 0.

— In the array, all the indexes are present at the continuous memory location.

— If the number of initialized array element < Max_Element_Count of an array then rest of the uninitialized Indexes will automatically initialize to zero.

— The number of initialized array element must be less than the declared array size.

Size of array is equal to Max_Element_Count*sizeof(dataType).

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