How to do it…

1. Let's assume that there is an array, p, with five elements, as follows:

Figure 1.1

Now, suppose you want to enter a value, say 99, at the third position. We will write a C program that will give the following output:

Figure 1.2

Here are the steps to follow to insert an element in an array:

1. Define a macro called max and initialize it to a value of 100:

#define max 100

2. Define an array p of size max elements:

int p[max]

3. Enter the length of the array when prompted. The length you enter will be assigned to a variable n:

printf("Enter length of array:");
scanf("%d",&n);

4. A for loop will be executed prompting you to enter the elements of the array:

for(i=0;i<=n-1;i++ )
    scanf("%d",&p[i]);

5. Specify the position in the array where the new value has to be inserted:

printf("\nEnter position where to insert:");
scanf("%d",&k);

6. Because the arrays in C are zero-based, the position you enter is decremented by 1:

k--;

7. To create space for the new element at the specified index location, all the elements are shifted one position down:

for(j=n-1;j>=k;j--)
    p[j+1]=p[j];

8. Enter the new value which will be inserted at the vacated index location:

printf("\nEnter the value to insert:");
scanf("%d",&p[k]);

Here is the insertintoarray.c program for inserting an element in between an array:

#include<stdio.h>
#define max 100
void main()
{
    int p[max], n,i,k,j;
    printf("Enter length of array:");
    scanf("%d",&n);
    printf("Enter %d elements of array\n",n);
    for(i=0;i<=n-1;i++ )
        scanf("%d",&p[i]);
    printf("\nThe array is:\n");
    for(i = 0;i<=n-1;i++)
        printf("%d\n",p[i]);
    printf("\nEnter position where to insert:");
    scanf("%d",&k);
    k--;/*The position is always one value higher than the subscript, so it is decremented by one*/             
    for(j=n-1;j>=k;j--)
        p[j+1]=p[j];
    /* Shifting all the elements of the array one position down from the location of insertion */
    printf("\nEnter the value to insert:");
    scanf("%d",&p[k]);
    printf("\nArray after insertion of element: \n");
    for(i=0;i<=n;i++)
        printf("%d\n",p[i]);
}

Now, let's go behind the scenes to understand the code better.