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# Binary Search in C++ Standard Template Library (STL)

In this article, we are going to learn how to search an element from an array using binary_search() function of C++ Standard Template Library (STL)?
Submitted by IncludeHelp, on January 04, 2018

## Problem statement

Given an array and we have to search an element using binary_search(), which is a function of algorithm header of C++ Standard Template Library.

## C++ STL binary_search() function

It is a built-in function, which is used to search an element from an array using Binary Search Algorithm.

### Syntax

```binary_search(start_address, end_address, element_to_search);
```

### Parameter(s)

1. start_address - starting array element’s pointer
2. end_address - ending array element’s pointer
3. element_to_search - element to search

## Steps for Binary Search in C++

1. Declare and define an array
2. Sort the array (here, we are using sort() function to sort array in ascending order).
3. Find the element using binary_search() function.
4. Print the message with its index if it exists.

## C++ program to implement Binary Search

```#include <algorithm>
#include <iostream>

using namespace std;

// function to display array list
void dispArray(int arr[], int size) {
for (int i = 0; i < size; i++) cout << " " << arr[i];
cout << endl;
}

// main code for binary search
int main() {
int a[] = {10, 1, 20, 2, 30, 4};

// get array length
int arr_length = sizeof(a) / sizeof(int);

// print array
cout << "Array elements are: ";
dispArray(a, arr_length);

// sort the array
sort(a, a + arr_length);
cout << "Sorted array elements: ";
dispArray(a, arr_length);

// searching 30 in the array
if (binary_search(a, a + arr_length, 30))
cout << "Element found" << endl;
else

return 0;
}
```

### Output

```Array elements are:  10 1 20 2 30 4
Sorted array elements:  1 2 4 10 20 30
Element found
```