Insert value in array at position

Algorithm: insert a value at a given position

Let A be the array with N elements (positions 1 to N), MAX the capacity, POS the position and VAL the new value.

1. Start.
2. Read N and the elements A[1] … A[N].
3. Read POS and VAL.
4. If N = MAX or POS < 1 or POS > N + 1, display "insertion not possible" and stop (overflow check).
5. Set I = N.
6. Repeat while I ≥ POS: set A[I + 1] = A[I]; set I = I − 1. (shift elements to the right)
7. Set A[POS] = VAL.
8. Set N = N + 1.
9. Display A[1] … A[N].
10. Stop.

Example: A = 10 20 30 40 50, POS = 3, VAL = 99. The elements 30, 40, 50 move one place right and 99 is stored at position 3, giving 10 20 99 30 40 50.

C implementation of the same algorithm:

#include <stdio.h>

int main(void)
{
    int a[50], n, pos, val;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter elements: ");
    for (int i = 0; i < n; i++)
        scanf("%d", &a[i]);
    printf("Enter position (1 to %d) and value: ", n + 1);
    scanf("%d %d", &pos, &val);

    if (n >= 50 || pos < 1 || pos > n + 1) {
        printf("Insertion not possible\n");
        return 1;
    }
    for (int i = n - 1; i >= pos - 1; i--)   /* shift right */
        a[i + 1] = a[i];
    a[pos - 1] = val;
    n++;

    printf("New array: ");
    for (int i = 0; i < n; i++)
        printf("%d ", a[i]);
    printf("\n");
    return 0;
}

Output:

Input: 5 10 20 30 40 50 3 99

Enter number of elements: Enter elements: Enter position (1 to 6) and value: New array: 10 20 99 30 40 50