### Insertion and Deletion of elements in an Array

Suppose you are storing temperature data for a few months and you forgot to store the temperature of a particular day (say 5th day) then you need to INSERT that temperature after the 4th element of the array and in the other case if you accidentally stored duplicate data then you need to DELETE the duplicate element.

Apart from these simple examples, there are many other uses of insertion and deletion

The array to which the element is to be inserted or deleted can be of two types unordered (unsorted) and ordered (sorted). Here we will be discussing about the insertion and deletion of element in an unordered or unsorted array.

For insertion in these types of arrays, we need to have two information, the element to be inserted and the position to which it will be inserted. For deletion, we only need the position.

Suppose we have the following array:

arr[5]={5,7,2,1,3}

And we need to insert the element 6 at the 2nd position, after insertion:

arr[5]={5,6,7,2,1}

Notice how the last element of the array (i.e. 3) has gone out to compensate for the insertion.

Now, suppose we wish to delete the element at position 3rd, after deletion:

arr[5]={5,6,2,1,0}

We see, all the elements after the 3rd have shifted to their left and the vacant space is filled with 0.

That’s exactly how insertion and deletion are done!

Algorithm for Insertion of an element in an array

Suppose, the array to be arr[max], pos to be the position at which the element num has to be inserted. For insertion, all the elements starting from the position pos are shifted towards their right to make a vacant space where the element num is inserted.

1. ```FOR I = (max-1) TO pos
arr[I] = arr[I-1]```
2. ` arr[I] = num`

Yeah it is that simple!

Algorithm for Deletion of an element in an array

Suppose, the array to be arr[max], pos to be the position from which the element has to be deleted. For deletion, all the elements to the right of the element at position pos are shifted to their left and the last vacant space is filled with 0.

1. ```FOR I = pos TO (max-1)
arr[I-1] = arr[I]```
2. `arr[I-1] = 0`

Now, to illustrate all this let me show you a simple example program:

```  // Example Program to illustrate
// insertion and deletion of
// elements in an array

#include<iostream.h>

// array has been declared as
// global so that other functions
int arr[5];

// function prototype
void a_insert(int, int);
void a_delete(int);

void main(void)
{
int ch;
int num,pos;

while(ch!=4)
{
cout<<"1> Insert";
cout<<"\n2> Delete";
cout<<"\n3> Show";
cout<<"\n4> Quit\n";

cin>>ch;

switch(ch)
{
case 1:
cout<<"enter element:";
cin>>num;
cout<<"enter pos.:";
cin>>pos;

a_insert(num,pos);
break;

case 2:
cout<<"enter pos.:";
cin>>pos;
a_delete(pos);
break;

case 3:
cout<<"\nArray:";
for(int i=0;i<5;i++)
cout<<arr[i]<<" ";
break;
}
cout<<"\n";
}
}

// insertion function
void a_insert(int num, int pos)
{
for(int i=4; i>=pos;i--)
arr[i]=arr[i-1];
arr[i]=num;
}```
```  // deletion function
void a_delete(int pos)
{
for(int i=pos; i<=4;i++)
arr[i-1]=arr[i];
arr[i-1]=0;
}```

Good-Bye!

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