How to insert an element in order given an array? - c

Question

Let us assume we have the following numbers in an array: 1, 3, 6, 15
If the user inputs a certain integer such as the number 5, than how could you have it inserted in the correct order in the above array so that you could print the following new array:
1, 3, 5, 6, 15. The array to be used is a variable length array and we are assuming that the user enters the numbers of the array in a sorted and non-decreasing order, so there is no need for sorting but just to insert an element (also entered by user) in the correct place. Below I have the code as to how far I got because I don't know what command to use to do the insertion of x into the array, and I am a newbie to C programming.
#include <stdio.h>
int insertion_array (int n, int ary[*]);
int main (void)
{
int n; // size
int x; // The element to be inserted in the array
int i, j;
printf("Enter size of array: ");
scanf("%d", &n);
printf("Enter the value of x: ");
scanf("%d", &x);
int ary[n];
for(i = 0; i < n; i++)
{
printf("Enter number %d: ", i + 1);
scanf("%d", &ary[i]);
} // for
return 0;
} // main

Answer 1

I could come up with a simple O(n) algorithm:
use binary search to find the place to insert, say position 5
shift all numbers after position 5 right
assign position 5 to the new integer
But there are O(lgn) algorithm for insertion, say AVL-tree, RB-tree and etc. But are much more complicated.
#include <stdio.h>
#include <stdlib.h>
int binsearch(int *arr, int size, int key)
{
int low = 0, high = size - 1;
if (key > arr[high]) return size;
while (high > low) {
int mid = (low + high) / 2;
if (arr[mid] > key) high = mid;
else low = mid + 1;
}
return low;
}
int main()
{
int size = 10;
int *arr = (int *)malloc(size * sizeof(int));
int elem, len = 0;
arr[len++] = 0;
while (scanf("%d", &elem) != EOF) {
int pos = binsearch(arr, len, elem);
printf("%d\n", pos);
int i;
for (i = len-1; i >= pos; --i)
arr[i+1] = arr[i];
arr[pos] = elem;
++len;
for (i = 0; i < len; ++i)
printf("%d ", arr[i]);
printf("\n");
}
free(arr);
return 0;
}