I am trying to carry out a binary search to find the index of a specific element within the vector. I tried getting the first and last element and passing them to the variable high and low. I am getting some sort of conversion error. The error is below inside the BinarySearchVector funtion.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

    int limit=10;
    vector <int> elements; 
    void AddValueToVector(){
        cout<<"Hello World:"<<endl;
        for (int i = 0; i < limit; i  )
        {
            int a;
            cin>>a;
            elements.push_back(a);
        }   
        
    }
    void printContents(){
        cout<<"Vector elements:"<<endl;
        for (int j = 0; j < limit; j  )
        {
            cout<<elements[j]<<endl;
        }   
    }

    int binarySearchVector(vector<int>&elements,int searchval){
        sort(elements.begin(),elements.end());

        auto low= elements.begin();
        auto high= elements.end();
         while (low <= high) {
            int mid = low   (high - low) / 2;

            if (elements[mid] == searchval)
            return mid;

            if (elements[mid] < searchval)
            low = mid   1;

            else
            high = mid - 1;
        }
        return -1;     
    }

    void search(){
        int searchval;
        cout<<"Enter value to search:"<<endl;
        cin>>searchval;
        int result= binarySearchVector(elements,searchval);
        if (result==-1)
        {
            cout<<"Not Found"<<endl;
        }else{
            cout<<"Element is found at index"<<result<<endl;
        }
        
    }
 
int main()
{
    AddValueToVector();
    printContents();
    search();
    return 0;
}

Any recommendations will be greatly appreciated.

CodePudding user response：

To use the binary search method you need to sort the vector.

The variables low and high are iterators

    auto low= elements.begin();
    auto high= elements.end();

There is no implicit conversion an iterator to an object of the type int that you are trying to do

     while (low <= high) {
        int mid = low   (high - low) / 2;
        //... 

You need to write at least

        auto mid = low   (high - low) / 2;

or

        auto mid = std::next( low,  std::distance( low, high ) / 2 );
    

Moreover the condition in the loop

     while (low <= high) {

is incorrect for an empty vector. You need to write

     while (low < high) {

CodePudding user response：

You mean

int mid = *low   (*high - *low) / 2;

an iterator is effectively a pointer to the element. If you want the element itself you need to dereference it

CodePudding user response：

Since your binarySearchVector function is supposed to return the index of the found element (not an iterator) you should probably not use begin() and end() (that return iterators, not indices).

Example:

int binarySearchVector(std::vector<int>& elements, int searchval) {
    std::sort(elements.begin(), elements.end());

    int low = 0;                    // index of first element
    int high = elements.size() - 1; // index of last element
    
    while (low <= high) {
        int mid = low   (high - low) / 2;

        if (elements[mid] < searchval)
            low = mid   1;
        else if (elements[mid] > searchval)
            high = mid - 1;
        else
            return mid;
    }
    return -1;
}