binary_search.cpp

// Binary Search implemented in C++
// Carlos Abraham Hernandez
// algorithms.abranhe.com/searches/binary-search
// repl.it/@abranhe/Binary-Search

#include <iostream>
using namespace std;

int binary_search(int a[],int l,int r,int key)
{
	while(l<=r)
  {
		int m = l + (r-l) / 2;

		if(key == a[m])
			return m;
		else if(key < a[m])
			r = m-1;
		else
			l = m+1;
	}
	return -1;
}

int main(int argc, char const *argv[])
{
	int n, key;
	cout << "Enter size of array: ";
	cin >> n;
	cout << "Enter array elements: ";
	int a[n];
	
  for (int i = 0; i < n; ++i)
	{
		cin>>a[i];	
	}
	cout << "Enter search key: ";
	cin>>key;	
	
  int res = binary_search(a, 0, n-1, key);
	
  if(res != -1)
		cout<< key << " found at index " << res << endl;
	else
		cout << key << " not found" << endl;
	return 0;
}