Array in C - Declare Initialize Access and Operations

Here We learn Array in C how to Declare Initialize and access array and operations on array.

Array is a data structure that can store elements of the same type.

Array is a collection of similar type elements

It stores the elements in a contiguous memory locations.

1 Why Array Required?

Array is used to store similar types of values under same name

We want to declare 100 integer variable

Instead of declaring 100 individual variables, such as

int number0, number1,number2,number3, ... …., number99;

you can declare one integer array variable such as

int number[100];

here number[100] is an integer array of size 100, means this array can store 100 integer value.

Array indexing starts from index 0 to n-1. Means first integer number store in array number[0], second integer number store in array number[1], third integer number store in array number[2], and so on. Here 100^th number store in array numbers[99].

2 How to Declare an Array in C?

Syntax of declare an array in C is as below

DataType arrayName [ arraySize ];

This is called a single-dimensional array.

DataType : any valid C data type like int, char, float, double, long
array Name: Any valid c identifier
arraySize: an integer constant greater than zero.

For Instance

int age[5];
long length[8];
float price[7];
double value[5];
char ch[5];

Above all are example of array.

age is a integer array of size 5.
length is a long array of size 8
price is a float array of size 7
value is double array of size 5
ch is a character array of size 5

Size tells us that a array can store maximum element up to size.

Size must be a integer constant. based on size array occupies memory location for elements.

There are multi dimensional array.

3 Array Initialization

Giving initial value to array is know as array initialization.

A Initializing each member

We can initialize each element one by one as below.

int age[5]; //declaration

age[0]=21; age[1]=24; age[2]=25; age[3]=27; age[4]=26;

Array uses zero based indexing so first element is stored in age[0] and last element will store in size-1 position here age[4];

B Declare and initialize

general syntax is

DataType arrayName[size]={value1,value2,.............,valueN};

example

int age[5]={21,24,25,27,26};

value 21 will store in age[0] and value 24 will store in age[1] and similar for other values.

While initializing array giving size is optional;

float price[]={22.2,44.2,67.33,55.66,43.2};

Some times we want to initialize only few elements of array in that case we have to provide size of array and initialize only few values other values are initialized by zero.

double value[20]={10.0,21.0};

Here from value[3] to value[19] will be initialize by 0.0

4 Access Array Elements

Array uses zero based indexing to access elements.

to access element of an array, we can use syntax

arrayName[index];

int age[5]={21,24,25,27,26};

age[0], age[1],age[2],age[3],age[4], will access 21,24,25,27 and 26 respectively.

Lets see few examples to store values in array and access array values.

Example: write a program to create integer array and store 5 integer number and print.

#include <stdio.h>
#include<stdio.h>
int main()
{
        int num[5]; // array num can store 5 integer value

        num[0] = 20; // store 20 at array index 0			
        num[1] = 11; // store 11 at array index 1			
        num[2] = 20; // store 20 at array index 2			
        num[3] = 33; // store 33 at array index 3			
        num[4] = 55; // store 55 at array index 55

        printf("\nnum[0] = %d" , num[0]);
        printf("\nnum[1] = %d", num[1]);
        printf("\nnum[2] = %d" , num[2]);
        printf("\nnum[3] = %d", num[3]);
        printf("\nnum[4] = %d" , num[4]);						
return 0;
}

#include <stdio.h>

#include<stdio.h>

int main()

{

int num[5]; // array num can store 5 integer value

num[0] = 20; // store 20 at array index 0

num[1] = 11; // store 11 at array index 1

num[2] = 20; // store 20 at array index 2

num[3] = 33; // store 33 at array index 3

num[4] = 55; // store 55 at array index 55

printf("\nnum[0] = %d" , num[0]);

printf("\nnum[1] = %d", num[1]);

printf("\nnum[2] = %d" , num[2]);

printf("\nnum[3] = %d", num[3]);

printf("\nnum[4] = %d" , num[4]);

return 0;

}

num[0] = 20
num[1] = 11
num[2] = 20
num[3] = 33
num[4] = 55

num[0] = 20

num[1] = 11

num[2] = 20

num[3] = 33

num[4] = 55

Description : In the above program, int num[5] array can store 5 element in a contiguous memory locations from index 0 to 4.

Example: write a program to take 5 number from user and store integer number in integer array and print.

#include <stdio.h>
#include<stdio.h>
int main() {

    int i;
    int num[5]; // array num can store 5 integer value	
    printf("Enter 5 integer number");
    for (i = 0; i < 5; i++) // for loop to take 5 integer number from user

    {
        scanf("%d", & num[i]);
    }
    printf("\n Entered number is");
    for (i = 0; i < 5; i++) // for loop to take 5 integer number from user	
    {
        printf("\n num[%d] =%d", i, num[i]);
    }

    return 0;
}

#include <stdio.h>

#include<stdio.h>

int main() {

int i;

int num[5]; // array num can store 5 integer value

printf("Enter 5 integer number");

for (i = 0; i < 5; i++) // for loop to take 5 integer number from user

{

scanf("%d", & num[i]);

}

printf("\n Entered number is");

for (i = 0; i < 5; i++) // for loop to take 5 integer number from user

{

printf("\n num[%d] =%d", i, num[i]);

}

return 0;

}

OUTPUT

Enter 5 integer number
21		// enter by user
32
33
44
35
 Entered number is
 num[0] =21
 num[1] =32
 num[2] =33
 num[3] =44
 num[4] =35

Enter 5 integer number

21 // enter by user

Entered number is

num[0] =21

num[1] =32

num[2] =33

num[3] =44

num[4] =35

Example: Print the sum of all elements of an array

#include<stdio.h>
int main() {
   int marks[]={88,91,93,90,86,89};
   int i,sum=0;
   for(i=0;i<6;i++){
       sum+=marks[i];
   }
   printf("Total marks : %d ",sum);
}

#include<stdio.h>

int main() {

int marks[]={88,91,93,90,86,89};

int i,sum=0;

for(i=0;i<6;i++){

sum+=marks[i];

}

printf("Total marks : %d ",sum);

}

Output

Total marks : 537

1	Total marks : 537

5 Operations on Array

On array we can perform following basic operations

Traverse– accessing all element of array
Insertion– adding a new element at specified position
Update – changing the existing value at specified position
Deletion– deleting an element from specified position
Search– search a element in array

A Traverse an array

Traversing is accessing the element of array.

Here we will access each element and print it

#include<stdio.h>

int main() {
   int age[]={22,23,26,29,21,20};
   int i;
   for(i=0;i<6;i++){
       printf("age[%d]=%d\n",i,age[i]);
   }
}

#include<stdio.h>

int main() {

int age[]={22,23,26,29,21,20};

int i;

for(i=0;i<6;i++){

printf("age[%d]=%d\n",i,age[i]);

}

Output

age[0]=22
age[1]=23
age[2]=26
age[3]=29
age[4]=21
age[5]=20

age[0]=22

age[1]=23

age[2]=26

age[3]=29

age[4]=21

age[5]=20

B. Inserting an element in Array

add a new element in array can be done at various position

Insertion at the beginning of array
add at the give index position
Insert at last

Here we will insert a element based on index position.

On inserting a new element at specified position next element will move one space forward in array.

#include<stdio.h>

int main() {
    int arr[] = {22, 23, 26, 29, 21, 20};
    int i, j, position = 0, element = 0;
    int arraySize =sizeof(arr)/sizeof(int); 
    printf("Array is \n");
    for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
    printf("\nEnter index position on which you insert new element\n");
    scanf("%d", &position);
    printf("\nEnter element to insert\n");
    scanf("%d", &element);
    if(position<=arraySize){
   /*move all element one place forward from user insertion position*/
    for (j = arraySize; j >= position; j--) {
          arr[j + 1] = arr[j];
    }
    /*insert element at specified position*/
    arr[position]=element;
    /*incrementing array size*/
    arraySize++;
    /*printing all elements*/
    printf("Array after inserting element\n");
    for (i = 0; i < arraySize; i++) {
         printf("arr[%d]=%d  ", i, arr[i]);
    }
    }else{
        printf("Please enter a valid position between 0 to %d",arraySize);
    }
    }

#include<stdio.h>

int main() {

int arr[] = {22, 23, 26, 29, 21, 20};

int i, j, position = 0, element = 0;

int arraySize =sizeof(arr)/sizeof(int);

printf("Array is \n");

for (i = 0; i < arraySize; i++) {

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

}

printf("\nEnter index position on which you insert new element\n");

scanf("%d", &position);

printf("\nEnter element to insert\n");

scanf("%d", &element);

if(position<=arraySize){

/*move all element one place forward from user insertion position*/

for (j = arraySize; j >= position; j--) {

arr[j + 1] = arr[j];

}

/*insert element at specified position*/

arr[position]=element;

/*incrementing array size*/

arraySize++;

/*printing all elements*/

printf("Array after inserting element\n");

for (i = 0; i < arraySize; i++) {

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

}

}else{

printf("Please enter a valid position between 0 to %d",arraySize);

}

Output

Array is 
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=29  arr[4]=21  arr[5]=20  
Enter index position on which you insert new element
1
Enter element to insert
99
Array after inserting element
arr[0]=22  arr[1]=99  arr[2]=23  arr[3]=26  arr[4]=29  arr[5]=21  arr[6]=20

Array is

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=29 arr[4]=21 arr[5]=20

Enter index position on which you insert new element

Enter element to insert

Array after inserting element

arr[0]=22 arr[1]=99 arr[2]=23 arr[3]=26 arr[4]=29 arr[5]=21 arr[6]=20

C Update an element in Array

To update an array element we have to select element based on index value and provide new value to replace the existing one.

Simple program to update array value based on index is as below

#include<stdio.h>

int main() {
    int arr[] = {22, 23, 26, 29, 21, 20};
    int i, j, position = 0, element = 0;
    int arraySize =sizeof(arr)/sizeof(int); 
    printf("Array is \n");
    for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
    printf("\nEnter index position on which you want to update element\n");
    scanf("%d", &position);
    printf("\nEnter element to insert\n");
    scanf("%d", &element);
    if(position<arraySize){
   
    /*update element at specified position*/
    arr[position]=element;
    /*printing all elements*/
    printf("Array after updating element\n");
    for (i = 0; i < arraySize; i++) {
         printf("arr[%d]=%d  ", i, arr[i]);
    }
    }else{
        printf("Please enter a valid position between 0 to %d",arraySize-1);
    }
    }

#include<stdio.h>

int main() {

int arr[] = {22, 23, 26, 29, 21, 20};

int i, j, position = 0, element = 0;

int arraySize =sizeof(arr)/sizeof(int);

printf("Array is \n");

for (i = 0; i < arraySize; i++) {

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

}

printf("\nEnter index position on which you want to update element\n");

scanf("%d", &position);

printf("\nEnter element to insert\n");

scanf("%d", &element);

if(position<arraySize){

/*update element at specified position*/

arr[position]=element;

/*printing all elements*/

printf("Array after updating element\n");

for (i = 0; i < arraySize; i++) {

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

}

}else{

printf("Please enter a valid position between 0 to %d",arraySize-1);

}

Output

Array is 
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=29  arr[4]=21  arr[5]=20  
Enter index position on which you want to update element

Array after updating element
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=2  arr[4]=21  arr[5]=20

Array is

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=29 arr[4]=21 arr[5]=20

Enter index position on which you want to update element

Array after updating element

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=2 arr[4]=21 arr[5]=20

D Delete an element in Array

To delete an array element First select index value of element.

After deleting array element other elements are shifted forward to fill the gap of deleted element.

#include<stdio.h>

int main() {
    int arr[] = {22, 23, 26, 29, 21, 20};
    int i, j, position = 0, element = 0;
    int arraySize =sizeof(arr)/sizeof(int); 
    printf("Array is \n");
    for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
    printf("\nEnter index position to delete element\n");
    scanf("%d", &position);
    if(position<arraySize){
   /*move all element one place backward position*/
    for (j = position; j <arraySize; j++) {
          arr[j] = arr[j+1];
    }
   
   /*decrement array size*/
    arraySize--;
    /*printing all elements*/
    printf("Array after deleting element\n");
    for (i = 0; i < arraySize; i++) {
         printf("arr[%d]=%d  ", i, arr[i]);
    }
    }else{
        printf("Please enter a valid position between 0 to %d",arraySize-1);
    }
    }

#include<stdio.h>

int main() {

int arr[] = {22, 23, 26, 29, 21, 20};

int i, j, position = 0, element = 0;

int arraySize =sizeof(arr)/sizeof(int);

printf("Array is \n");

for (i = 0; i < arraySize; i++) {

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

}

printf("\nEnter index position to delete element\n");

scanf("%d", &position);

if(position<arraySize){

/*move all element one place backward position*/

for (j = position; j <arraySize; j++) {

arr[j] = arr[j+1];

}

/*decrement array size*/

arraySize--;

/*printing all elements*/

printf("Array after deleting element\n");

for (i = 0; i < arraySize; i++) {

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

}

}else{

printf("Please enter a valid position between 0 to %d",arraySize-1);

}

Output

Array is 
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=29  arr[4]=21  arr[5]=20  
Enter index position to delete element
2
Array after inserting element
arr[0]=22  arr[1]=23  arr[2]=29  arr[3]=21  arr[4]=20

Array is

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=29 arr[4]=21 arr[5]=20

Enter index position to delete element

Array after inserting element

arr[0]=22 arr[1]=23 arr[2]=29 arr[3]=21 arr[4]=20

E Search an element in Array

Search operation is used to find an element in array.

If element fond return index and element value.

If not it will return -1.

#include<stdio.h>

int main() {
    int arr[] = {22, 23, 26, 29, 21, 20};
    int i, j, position = -1, element = 0;
    int arraySize =sizeof(arr)/sizeof(int); 
    printf("Array is \n");
    for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
    printf("\nEnter element to search in array\n");
    scanf("%d", &element);
   
   /*checking element one by one*/
    for (j =0; j <arraySize; j++) {
          if(arr[j]==element)
          position=j;
          break;
    }
   if(position>=0){
       printf("You searched for arr[%d]=%d",position,element);
       
   }else{
       printf("Element not found");
   }
   
    }

#include<stdio.h>

int main() {

int arr[] = {22, 23, 26, 29, 21, 20};

int i, j, position = -1, element = 0;

int arraySize =sizeof(arr)/sizeof(int);

printf("Array is \n");

for (i = 0; i < arraySize; i++) {

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

}

printf("\nEnter element to search in array\n");

scanf("%d", &element);

/*checking element one by one*/

for (j =0; j <arraySize; j++) {

if(arr[j]==element)

position=j;

break;

}

if(position>=0){

printf("You searched for arr[%d]=%d",position,element);

}else{

printf("Element not found");

}

Output

Array is 
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=29  arr[4]=21  arr[5]=20  
Enter element to search in array 
22
You searched for arr[0]=22

Array is

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=29 arr[4]=21 arr[5]=20

Enter element to search in array

You searched for arr[0]=22

F Sorting elements in Array

Arranging array elements in ascending or in descending order is known as sorting of array.

Following program is used to sort array elements in ascending order.

#include<stdio.h>

int main() {
    int arr[] = {22, 23, 26, 29, 21, 20};
    int i, j,temp=0;
    int arraySize =sizeof(arr)/sizeof(int); 
    printf("Array is \n");
    for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
    
    for(i=0;i<arraySize;i++){
        for(j=i+1;j<arraySize;j++){
           if(arr[i]>arr[j]){
            temp=arr[i];
            arr[i]=arr[j];
            arr[j]=temp;
           }
        }
    }
    /*sorted array is*/
    printf("\nSorted array is\n");
     for (i = 0; i < arraySize; i++) {
        printf("arr[%d]=%d  ", i, arr[i]);
    }
}

#include<stdio.h>

int main() {

int arr[] = {22, 23, 26, 29, 21, 20};

int i, j,temp=0;

int arraySize =sizeof(arr)/sizeof(int);

printf("Array is \n");

for (i = 0; i < arraySize; i++) {

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

}

for(i=0;i<arraySize;i++){

for(j=i+1;j<arraySize;j++){

if(arr[i]>arr[j]){

temp=arr[i];

arr[i]=arr[j];

arr[j]=temp;

}

/*sorted array is*/

printf("\nSorted array is\n");

for (i = 0; i < arraySize; i++) {

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

}

Output

Array is 
arr[0]=22  arr[1]=23  arr[2]=26  arr[3]=29  arr[4]=21  arr[5]=20  
Sorted array is
arr[0]=20  arr[1]=21  arr[2]=22  arr[3]=23  arr[4]=26  arr[5]=29

Array is

arr[0]=22 arr[1]=23 arr[2]=26 arr[3]=29 arr[4]=21 arr[5]=20

Sorted array is

arr[0]=20 arr[1]=21 arr[2]=22 arr[3]=23 arr[4]=26 arr[5]=29