Binary Search functions in C++ STL (binary_search, lower_bound and upper_bound)

// C++ code to show how to use the binary_search()
// for searching an element in the given range
#include <bits/stdc++.h>
using namespace std;

// Function for check an element whether it
// is present or not
void isPresent(vector<int> &arr, int val) {
  
    // using binary_search to check if val exists
    if (binary_search(arr.begin(), arr.end(), val))
        cout << val << " exists in vector";
    else
        cout << val << " does not exist";

    cout << endl;
}

int main() {
    vector<int> arr = {10, 15, 20, 25, 30, 35};

    int val1 = 15;
    int val2 = 23;

    isPresent(arr, val1);
    isPresent(arr, val2);

    return 0;
}

// C++ Program to show how to use std::lower_bound()
#include <bits/stdc++.h>
using namespace std;

int main() {

    vector<int> arr1 = {10, 15, 20, 25, 30, 35};
    vector<int> arr2 = {10, 15, 20, 20, 25, 30, 35};
    vector<int> arr3 = {10, 15, 25, 30, 35};
  
    int val = 20;

    // using lower_bound() to check if val exists
    // in arr1, single occurrence, prints 2
    cout << lower_bound(arr1.begin(), arr1.end(), val)
      - arr1.begin();
    cout << endl;

    // using lower_bound() to check if val exists
    // in arr2, multiple occurrence , prints 2
    cout << lower_bound(arr2.begin(), arr2.end(), val)
      - arr2.begin();
    cout << endl;

    // using lower_bound() to check if val exists
    // in arr3, no occurrence , prints 2 
    // ( index of next higher)
    cout << lower_bound(arr3.begin(), arr3.end(), val)
      - arr3.begin();
    cout << endl;
  return 0;
}

// C++ code to show the working of std::upper_bound()
#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> arr1 = {10, 15, 20, 25, 30, 35};
    vector<int> arr2 = {10, 15, 20, 20, 25, 30, 35};
    vector<int> arr3 = {10, 15, 25, 30, 35};
  
    int val = 20;

    // using upper_bound() to check if val exists
    // in arr1, single occurrence, prints 3
    cout << upper_bound(arr1.begin(), arr1.end(), val)
      - arr1.begin();
    cout << endl;

    // using upper_bound() to check if val exists
    // in arr2, multiple occurrence, prints 4
    cout << upper_bound(arr2.begin(), arr2.end(), val)
      - arr2.begin();
    cout << endl;

    // using upper_bound() to check if val exists
    // in arr3, no occurrence,  prints 2 
    // ( index of next higher)
    cout << upper_bound(arr3.begin(), arr3.end(), val)
      - arr3.begin();
    cout << endl;
  return 0;
}