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Binary Search Program in C, C++

Write a C, C++ program to implement a binary search. Binary search is an efficient search algorithm as compared to linear search.  Let's implement this algorithm in  C, C++.

Binary Search


Binary search is a search algorithm that finds the position of an element (target value) within a sorted array. It is also known as half-interval search or logarithmic search.

Important Points

i) Always use binary search with sorted values (either in asc or desc order).

Bubble sort algorithm and their implementation

Quicksort algorithm and their implementation

ii) Time complexity of binary search.

      Best case performance - O(1)

      Average and worst case time complexity - O(nlogn)


Binary Search using Recursion in C, C++

Sorting algorithm and their time complexity

Binary Search Algorithm


    low = 0;
    high = size - 1;
    
    while (low <= high) {
     
        /* Calculate mid index */

        mid = (low + high) / 2;
    
        /* If element is found at mid index
           then return the index */

        if (arr[mid] == num ) {
         
            return mid+1;
         
        } else if ( arr[mid] > num) {
         
            high = mid - 1;
         
        } else if ( arr[mid] < num) {
         
            low = mid + 1;
         
        }
    }

    /* If element is not found return -1 */

    return -1;
  

Binary Search Program in C++


#include<iostream.h>
#include<conio.h>

void main()
{

   int arr[100],beg,mid,end,i,n,num;

   cout << "\n Enter the size of an array ";
   cin >> n;

   cout << "\n Enter the values in sorted order (asc or desc) \n";

   for(i = 0; i < n;i++)
   {   
       cin >> arr[i];
   }   

  
   /* Initialize beg and end value. */

   beg = 0;
   end = n-1;

   cout << "\n Enter a value to be searched in an array ";
   cin >> num;

   /* Run loop, while beg is less than end. */

   while( beg <= end)
   {   
       
      /* Calculate mid. */
        
      mid = (beg+end)/2;

     /* If value is found at mid index,
        the print the position and exit. */

      if(arr[mid] == num)
      {   
         cout << "\nItem found at position "<< (mid+1);
   
          exit(0);

      } else if(num > arr[mid]) {

         beg=mid+1;

      } else if (num < arr[mid]) {

         end=mid-1;
 
      }

   }

    cout << "Number does not found.";
 }

Output:

Enter the size of an array : 7

Enter the values in sorted order (asc or desc) :

3    5    6    8   9   12  13

Enter a value to be search :  6

Item found at position : 3

Binary Search Program in C


#include <stdio.h>

/* Search number in an array using binary search algorithm */

int binarySearch (int arr[], int num, int size) {

    int low, high, mid;
    
    low = 0;
    high = size - 1;
    
    while (low <= high) {
     
        /* Calculate mid index */

        mid = (low + high) / 2;
    
        /* If element is found at mid index 
           then return the index */

        if (arr[mid] == num ) {
         
            return mid+1;
         
        } else if ( arr[mid] > num) {
         
            high = mid - 1;
         
        } else if ( arr[mid] < num) {
         
            low = mid + 1;
         
        }
    }
    
    return -1;
 
}

int main(void) {
    
   int arr[100], len, num, result;
 
   printf(" \n Enter the size of an array (Max 100)");
   scanf ("%d", &len);
 
   printf("\n Enter the elements of an array in asc or desc order");
 
   /* Taking array input values from user */
 
   for (int i = 0; i < len; i++) {
  
      scanf ("%d", &arr[i]);
  
   }
 
   printf ("\n Enter the elements to be searched in an array");
   scanf ("%d", &num);
 
   result = binarySearch (arr, num, len);
 
   if (result == -1) {
  
       printf (" \n Number is not found in an array");
  
   } else {
  
       printf (" \n Number is found at %d position", result );
   }
 
   return 0;
}

Output :

Enter the size of an array (Max 100) : 5

Enter the elements of an array in asc or desc order : 2   3    6   7   8

Enter the elements to be searched in an array : 7

Number is found at 4 position


Programming questions on Strings

Programming questions on Recursion

Programming questions on Array

Programming questions on Linked List

25 comments:

  1. i only understand binary search from this

    ReplyDelete
  2. I understand binary search only from this

    ReplyDelete
  3. What is the worst case of binary search Algorithm?

    ReplyDelete
    Replies
    1. Worst case of binary search occur when element you are searching is not present in array or list.

      Delete
  4. Replies
    1. What kind of help do you need in Binary Search program.

      Delete
  5. what is the expected output ?

    ReplyDelete
  6. is 'loc' of the input value not required to find the position ?

    ReplyDelete
  7. I couldn't figure out the last few lines of the code, pls help me

    ReplyDelete
  8. I couldn't figure out the logic of what happens if num>Arr[mid] pls help me!!

    ReplyDelete
    Replies
    1. If num > arr[mid] then set beg flag to mid + 1 as number is greater than mid so you will search the item in second halve.

      Delete
  9. No, choice of variable is our choice, we can choose any name of the variable

    ReplyDelete
  10. What about dealing with string arrays or char arrays??

    ReplyDelete
  11. this binary search code is wrong
    you can't write mid=(low+high)/2 . It will create overflow.Assume that you have an array of size 2^32 and low = 2^32-2 and high = 2^32-1 so low +high will create overflow .
    So the correct code will be mid = low+(high-low)/2;

    ReplyDelete
  12. Thanks man, it was great help!!

    ReplyDelete