binary search array 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: binary search function in c++

#include<iostream>
using namespace std;
int binarySearch(int arr[], int p, int r, int num) {
   if (p <= r) {
      int mid = (p + r)/2;
      if (arr[mid] == num)
      return mid ;
      if (arr[mid] > num)
      return binarySearch(arr, p, mid-1, num);
      if (arr[mid] > num)
      return binarySearch(arr, mid+1, r, num);
   }
   return -1;
}
int main(void) {
   int arr[] = {1, 3, 7, 15, 18, 20, 25, 33, 36, 40};
   int n = sizeof(arr)/ sizeof(arr[0]);
   int num = 33;
   int index = binarySearch (arr, 0, n-1, num);
   if(index == -1)
   cout<< num <<" is not present in the array";
   else
   cout<< num <<" is present at index "<< index <<" in the array";
   return 0;
}

Example 3: Binary search in c++

//By Sudhanshu Sharan
#include<iostream>
#include<cmath>
using namespace std;
// BCT= o(1)  and  WCT=O(logn)   time taken for unsucessful search is always o(logn)

int BinSearch( int arr[],int key,int len)
{
	int h,mid,l;
	l=0;
	h=len-1;
	while(l<=h)
	{
		mid=((l+h)/2);
		if(key==arr[mid])
			return mid;
		else if(key<arr[mid])
			h=mid-1;
		else
			l=mid+1;
	}
	return -1;
}
int main()
{
	int key,i,len;
	int arr[] = {1,2,3,6,9,12,15,34,54};
	len=sizeof(arr)/sizeof(arr[0]);
	cout<<"enter the key to be searched";
	cin>>key;
	int result= BinSearch(arr,key,len);
	(result == -1)
		? cout<<"Element is not present in the array"<<endl
		: cout<<"Element is present at index : "<<result<<endl;	
	for(i=0;i<len-1;i++)
		cout<<arr[i]<<" ";
    return 0;
}

Example 4: c++ binary search

int result = -1;
  int low = 0;
  int high = N-1; // N - # of elements
   while (low <= high)
   {  mid = (low + high) / 2;
      if ( item == vector[mid])
	  {  result = mid;
	     break; 
      }
      else if (item > vector[mid] )
	           { low =  mid + 1; }
          else  { high = mid - 1; }
   }