Question

I read a Pseudo Code of binary search in a data structure book and then I started to writing code. the code that i written is :

#include <iostream.h>
#include <conio.h>
template <class T>

int BSearch(T x[], const int n, T item)
    {
    int loc, first = 0, found = 0, last = n-1;
        while(first <= last && !found)
        {
            loc = (first + last)/2;
            if(item < x[loc])
                last = loc - 1;
            else if(item > x[loc])
                first = loc + 1;
            else
                found = 1;
         }
      return found;
   }

int main()
    {
    const int n =5;
      int x[n],item;
      cout << "Pls enter " <<n<<" number(s): ";

      for(int i = 0; i < n;i++)
        cin >> x[i];
      cout << "Pls enter the item to Search: ";
        cin >> item;
      if(BSearch(x,n,item))
        cout << "\n\t Item Exist";
      else
        cout << "\n\t Item NOT Exist";

      getch();
      return 0;
   }

there is no any Error but a logic fault is there . it just return 0 value from BSearch function and i just get this message “Item NOT Exist”. where is my bug ?! i didn’t find it.
Thanks

Answer 1

The binary search only works for ordered lists. But you don’t order the list you get from std::cin, therefore you get wrong results from your binary search.

To fix this you either have to restrict the input to pre-ordered lists, or you have to initially order your list before doing the binary search.