Binary search code cannot find the A[0] element of the array

Question

So, whenever i try to search for A[0] element(23 in this case). It don't return the position of the element. However, it works fine when i try to search for other elements then A[0]. Please tell what is wrong with the code and how can i fix it. Sample Output-- Enter item to search- 23 output- Element 23 could not be found in this array. Thanks in advance!

#include <iostream>
using namespace std;
int main(){
    int A[]= {23, 34, 45, 67, 75, 89};
    int I= sizeof(A)/sizeof(A[0]);
    int LAST= I-1, FIRST= 0, MID, ITEM, INDEX= 0;
    MID= ((FIRST + LAST)/2);
    cout<<"Enter item to search- ";
    cin>>ITEM;
    while(FIRST <= LAST){
        if(A[MID] == ITEM){
            INDEX= MID;
            break;
        }
        else if(A[MID] < ITEM){
            FIRST= MID+1;
        }
        else{
            LAST= MID-1;
        }
        MID= ((FIRST + LAST)/2);
    }
    if(INDEX != 0){
        cout<<"\nElement "<<ITEM<<" found at position "<<(INDEX+1);
    }
    else{
        cout<<"\nElement "<<ITEM<<" could not be found in this array.";
    }
}

Why not use the standard library binary search algorithm, std::lower_bound? Ex. auto i = std::lower_bound(std::begin(A), std::end(A), item); if (i != std::end(A) && *i == item) index = i - std::begin(A); — Daniel Schepler
– Daniel Schepler, Commented Aug 27, 2017 at 16:16
Yes indeed sir. As a newbie in "Data Structures" i need to research on various libraries. And I also have to convert it into C. But thank you for the comment. — TroubleShooter
– TroubleShooter, Commented Aug 27, 2017 at 16:38

Srichandradeep C · Accepted Answer · 2017-08-27 16:00:48Z

2

 if(INDEX >= 0){
   cout<<"\nElement "<<ITEM<<" found at position ". 
           <<(INDEX+1);
  }

An index starts at 0 in an array. Hence, modify the IF condition to check for INDEX >= 0. If the input element is not found then INDEX will be returned as -1.

answered Aug 27, 2017 at 16:00

Srichandradeep C

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1 Comment

TroubleShooter Over a year ago

Thank you sir! that was spot on. And of course a stupid mistake.

akp · Accepted Answer · 2017-08-27 16:02:31Z

1

you have put if index!=0 condition but 23 is at index 0

answered Aug 27, 2017 at 16:02

akp

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