Vector error,a very confusing segmentation error? - c++

Question

So basically,I am doing a code which searches for an element of a vector inside a vector.While I thought of the approach , implementing it got me a segmentation error. I narrowed down the problem
In the code if I decomment the line in the for loop while commenting the above then all elements of B[i] are being displayed.Why then is a segmentation error being thrown. I think the binary_return is more or less correct and if I replace the line with
binary_return(A,0,A.size(),B[1])
then its working.
Here is the code:
#include<iostream>
#include<vector>
using namespace std;
int binary_return(vector<int> a,int start,int end,int seek)
{
int mid = (start+end)/2;
//cout<<start<<" "<<seek<<" "<<mid;
if(end!=start)
{
if(a[mid]==seek)
{
return mid;
}
else if(a[mid]>seek)
{
return binary_return(a,start,mid,seek);
}
else if(a[mid]<seek)
{
return binary_return(a,mid,end,seek);
}
}
else
return -1;
}
int main()
{
vector<int> A{1,3,6,9,23};
vector<int> B{1,4,23};
cout<<B[0]<<B[1]<<B[2];
for(int i=0;i<B.size();i++)
{
cout<<binary_return(A,0,A.size(),B[i]);
//cout<<binary_return(A,0,A.size(),B[0]);
}
return 1;
}

Answer 1

Your code is not handling the last case correctly and ends up in infinite recursion.
This unfortunately in C++ means that anything can happen (you're not guaranteed to get a meaningful error).
Add a debug print at the beginning of the function and you'll see in which cases you're entering infinite recursion.

Answer 2

You have infinite recursion in third if statment
The correct code if the following:
#include<iostream>
#include<vector>
using namespace std;
int binary_return(vector<int> a,int start,int end,int seek)
{
int mid = (start+end)/2;
//cout<<start<<" "<<seek<<" "<<mid;
if(end!=start)
{
if(a[mid]==seek)
{
return mid;
}
else if(a[mid]>seek)
{
return binary_return(a,start,mid,seek);
}
else if(a[mid]<seek)
{
// In your sample you forgot to add +1 (mid+1) for next start
return binary_return(a,mid+1,end,seek);
}
}
else
return -1;
}
int main()
{
vector<int> A{1,3,6,9,23};
vector<int> B{1,4,23};
for(int i=0;i<B.size();i++)
{
cout<<binary_return(A,0,A.size(),B[i]);
}
return 0;
}