Bin Search

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int bin_search(int *a, int n, int x)
{
    int low, mid, high;
    int sum_left, sum_right;

    low = 0;
    high = n - 1;

    while(low <= high)
    {
        mid = (high+low) / 2;
        sum_left = a[mid] + a[mid-1];
        sum_right = a[mid] + a[mid+1];

        if(sum_left == x)
            return mid-1;

        else if(sum_right == x)
            return mid;

        else if(sum_right < x)
            low = mid+1;

        else if(sum_right > x)
            high = mid-1;
    }

    return -1;
}

void main()
{
    int a[] = {-3, 8, 1, 9, 15, 10, 18,33,21}; // 5

    int result = bin_search(a, 9, 54);

    printf("Result %d\n", result);

}