Binary search in array is not working properly

Question

// function for binary search in array
#include <iostream>
using namespace std;
int binSrch(int arr[], int n, int key)
{
    int s = 0, e = n; // s for starting and e for ending
    int mid = (s + e) / 2;
    while (s <= e)
    {
        if (arr[mid] == key)
            return mid;
        else if (arr[mid] > key)
            e = mid - 1;
        else
            s = mid + 1;
    }
    return -1;
}
int main()
{
    int n, key;
    cout << "enter no. of elements" << endl;
    cin >> n;
    int arr[n];
    cout << "enter array " << endl;
    for (int i = 0; i < n; i++)
    {
        cin >> arr[i];
    }
    cout << "enter key" << endl;
    cin >> key;
    cout << binSrch(arr, n, key);
    return 0;
}

This code for binary searching in array does not work.

For some array the program gets stuck. I don't know what did wrong.

I entered input in sorted format.

PS C:\Users\anmol\Desktop\c++projectwork> g++ .\binSearchArrFun.cpp
PS C:\Users\anmol\Desktop\c++projectwork> ./a
enter no. of elements
6
enter array 
2
3
4
5
6
7
enter key
8

it just stuck here rather than giving -1

Answer 1

Assuming that you are passing n as the size of the array, you should give e = n-1 since arrays are 0-indexed based, that is where you are probably getting the wrong answer. And you also should calculate mid after each iteration, so it should be inside the while loop.

Also, you should do mid = s +(e-s)/2 to avoid overflow.