recursive binary search in c++ code example

Example 1: binary search program c++

#include <iostream>
using namespace std;

// This program performs a binary search through an array, must be sorted to work
int binarySearch(int array[], int size, int value) 
{   
    int first = 0,         // First array element       
    last = size - 1,       // Last array element       
    middle,                // Mid point of search       
    position = -1;         // Position of search value   
    bool found = false;        // Flag   
    while (!found && first <= last) 
    {      
        middle = (first + last) / 2;     // Calculate mid point      
        if (array[middle] == value)      // If value is found at mid      
    	{         
                found = true;         
                position = middle;      
        }      
        else if (array[middle] > value)  // If value is in lower half         
            last = middle - 1;      
        else         
            first = middle + 1;          // If value is in upper half   
    }   
    return position;
}
int main ()
{
    const int size = 5; // size initialization
    int array[size] = {1, 2, 3, 4, 5}; // declare array of size 10
    int value; // declare value to be searched for
    int result; // declare variable that will be returned after binary search

    cout << "What value would you like to search for? "; // prompt user to enter value
    cin >> value;
    result = binarySearch(array, size, value);

    if (result == -1) // if value isn't found display this message
        cout << "Not found\n";
    else  // If value is found, displays message
        cout << "Your value is in the array.\n"; 
  
    return 0;
}

Example 2: dichotomic search c++

using namespace std; 
  
// A recursive binary search function. It returns 
// location of x in given array arr[l..r] is present, 
// otherwise -1 
int binarySearch(int arr[], int l, int r, int x) 
{ 
    if (r >= l) { 
        int mid = l + (r - l) / 2; 
  
        // If the element is present at the middle 
        // itself 
        if (arr[mid] == x) 
            return mid; 
  
        // If element is smaller than mid, then 
        // it can only be present in left subarray 
        if (arr[mid] > x) 
            return binarySearch(arr, l, mid - 1, x); 
  
        // Else the element can only be present 
        // in right subarray 
        return binarySearch(arr, mid + 1, r, x); 
    } 
  
    // We reach here when element is not 
    // present in array 
    return -1; 
} 
  
int main(void) 
{ 
    int arr[] = { 2, 3, 4, 10, 40 }; 
    int x = 10; 
    int n = sizeof(arr) / sizeof(arr[0]); 
    int result = binarySearch(arr, 0, n - 1, x); 
    (result == -1) ? cout << "Element is not present in array"
                   : cout << "Element is present at index " << result; 
    return 0; 
}