Binary search not working for n = 1, 2 - c++

Question

This is my code for binary search, and n = no of elements in array
// Binary Search
// BUG: not working for n = 2
#include <iostream>
int main() {
const int n = 1;
int newlist[n];
std::cout << "Enter " << n;
std::cout << " elements in increasing order:\n";
for( int i = 0; i < n; ++i ) {
std::cin >> newlist[i];
}
int pos = 0, num;
std::cout << "Enter number:\n";
std::cin >> num;
std::cout << '\n';
int imin = 0, imax = n-1;
int imid = (n - 1)/2;
for( int i = 0; i < n; ++i ) {
imid = (imin + imax) / 2;
if( newlist[imid] == num ) {
pos = imid;
}
else if( newlist[imid] < num ) {
imin = imid+1;
}
else {
imax = imid-1;
}
}
if( pos != 0 ) {
std::cout << "Found at " << pos+1;
}
else {
std::cout << "Not found!\n";
}
return 0;
}
It does work for n > 2, but fails to give correct output for n <= 2, ie, gives Not found! output even for elements that were found.
I think one way would be to have a separate implementation for n <= 2, but that will become cumbersome! Please help.

Answer 1

Set your pos operator to -1 rather than 0. 0 represents your first index and since you output that the element has not been found for pos == 0 condition, your code is failing. You should set pos to -1 initially and check that itself for not found condition, if an element is found at pos = 0, that means the element exists at the first index.

Answer 2

First pos equal to 0 is correct value. Therefore set pos to -1 at the beginning and compare to -1 (or more commonly >= 0) when checking whether it was found.
Secondly, there are few items that should be changed because right now it's not that much binary search:
There is no reason to initialize mid before the loop, it's just temporary variable with the scope in loop block.
The condition for exiting the search is min > max, you don't need any additional counter, as it would run the loop always n times even if the value didn't exist. So change to while (min <= max) { ...
Last but not least, once you find the item, exit the loop immediately by break statement.

Answer 3

I don't think a for-loop is the control structure to go for here, because you want to finish when you've either found the correct item or when imin and imax are non-sensical.
In the implementation given, you don't even stop the loop when you have found the item and just confirm the found item "n-(number of iterations until item was found)" times.
Furthermore, with C++ arrays and vectors being 0-based, having position == 0 as the marker for "not found" is a bad idea; you could instead use an item from http://en.cppreference.com/w/cpp/types/numeric_limits, or n (since the indices go from 0 to n-1).
In theory, you could use pointer arithmetic to make your array 1-based, and I am assuming you haven't; I wouldn't recommend it. However, you're code snipped is missing the actual definition of the list.