Binary Search Results being very inconsistent

Question

Doing a coding exercise for school, where we have to utilize binary search to find the location of a value within an array. The output should generate the index location.

When testing it out it's very "hit and miss". Sometimes it will say when a value is there, other times when a value is clearly there it will come up with "Element is not present in array". Struggling to troubleshoot where the source of this inconsistency is coming from.

Any help/tips/advice would be greatly appreciated.

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

#define SIZE 10

int binarySearch(int array[], int starting, int ending, int searchKey)
{

if (ending >= starting)
{       
        int mid = starting + (ending - starting)/2;
        if (array[mid] == searchKey) return mid;
        if (array[mid] > searchKey) return binarySearch(array, starting, mid-1, searchKey);
        return binarySearch(array, mid+1, ending, searchKey);
}
return -1;
}

int main(void)
{
    int array[10],i;
    int searchKey;

    srand(time(NULL));
    for (i=0; i<10; i++)
    array[i]=rand()%100;

    printf("Array before sorting \n");
    for (i=0; i<10; i++)
    printf("%d \n", array[i]);
   
    printf("Enter a number to search\n");
    scanf("%d", &searchKey);

    int result = binarySearch(array, 0, SIZE-1, searchKey);
    (result == -1)? 

    //Displaying the results to the user
    printf("Element is not present in array")
    : printf("Element is present at index %d", result+1);
    
    return 0;
}

Answer 1

Binary search requires that the array is sorted.

See e.g. https://en.wikipedia.org/wiki/Binary_search_algorithm#:~:text=Binary%20search%20works%20on%20sorted,lower%20half%20of%20the%20array.

It says:

In computer science, binary search, also known as ...., is a search algorithm that finds the position of a target value within a sorted array.

You generate the array by doing:

for (i=0; i<10; i++)
    array[i]=rand()%100;

so it's obviously not a sorted array. Consequently binary search will not work.

You can use qsort on the array to sort it. If your not allow to change the array, you'll need another search-algorithm than binary search.