Binary Search Algorithm Implementation in C++

In this Program we need to implement binary search to find the existence of a search sequence in an array. The time complexity of Binary search is O(log(n)).

Required steps and pseudocodes

Begin
   BinarySearch() function has ‘arr’ the array of data and ‘n’ the number of values, start and end index, iteration count and b[0] be the element to be searched in the argument list.
   Increment the iteration counter and compare the item value with the a[mid].
   If item < a[mid] choose first half otherwise second half to proceed further.
   Return index value to main.
   In main(), sequentially compare the remaining items of search sequence to next items in the array.
   Print the index range of the sequence found.
End.

Example Code

#include<iostream>
using namespace std;
int BinarySearch(int a[], int start, int end, int item, int iter) {
   int i, mid;
   iter++;
   mid = start+ (end-start+1)/2;
   if(item > a[end] || item < a[start] || mid == end) {
      cout<<"\nNot found";
      return -1;
   } else if(item == a[mid]) {
      return mid;
   } else if(item == a[start]) {
      return start;
   } else if(item == a[end]) {
      return end;
   } else if(item > a[mid])
      BinarySearch(a, mid, end, item, iter);
      else
         BinarySearch(a, start, mid, item, iter);
   }
int main() {
   int n, i, flag=0, Bin, len = 9, a[10]={1, 7, 15, 26, 29, 35, 38, 40, 49, 51};
   cout<<"\nEnter the number of element in the search sequence: ";
   cin>>n;
   int b[n];
   for(i = 0; i < n; i++) {
      cin>>b[i];
   }
   Bin = BinarySearch(a, 0, len, b[0], 0);
   if (Bin == -1) {
      cout<<"\nNot found.";
      return 0;
   } else {
      for(i = Bin; i < n+Bin; i++)
         if(a[i] != b[i-Bin])
            flag = 4;
            if(flag == 4)
               cout<<"\nNot found.";
            else
               cout<<"\nSequence found between index "<<Bin<<" and "<<Bin+n<<".";
   }
   return 0;
}

Output

Enter the number of element in the search sequence: 4
15
26
29
35
Sequence found between index 2 and 6.