C++ what is position doing in this binary search function?

Question

int binarySearch(int array[], int size, int value) //value is the number you want to look for
{
int first = 0, // First array element
last = size - 1, // Last array element
middle, // Mid point of search
position = -1; // Position of search value
bool found = false; // Flag

int numOfRounds = 0;

while (!found && first <= last)
{
middle = (first + last) / 2; // Calculate mid point
if (array[middle] == value) // If value is found at mid
{
found = true;
position = middle;
cout << "value is found at mid" << endl;
cout << "it is found!" << endl;
}
else if (array[middle] > value) // If value is in lower half
{
last = middle - 1;
cout << "value is found at lower half" << endl;
numOfRounds++;
}
else
{
first = middle + 1; // If value is in upper half
cout << "value is found at upper half" << endl;
numOfRounds++;
}
if (!(array[middle] == value))
{
cout << "value is NOT found" << endl;
}

cout << "Number of rounds: " << numOfRounds << endl;
cout << "- - - - - - - - - - - - - - - - -" << endl;

}
return position;
}

Answer 1

<position> is used to store the index of array element that contains the value you were looking for. In case the search failed, the value of <position> will not be changed from its initial value which is -1. The function use <position> as its return value.

Answer 2

Well, position is initialized as -1 and the only place where it gets a value is when array[middle] == value, there it gets the value of middle.

So position returns the position(index) where the value is found, and -1 if not.

Kinda useless if you ask me cause you can just return middle immediatly when it is found but everyone their own thing I guess. ^^

Answer 3

You may want to simplify your code:

int last = size - 1;
if (size < 1)
return -1; // Error code

mid = last / 2;

while (last > -1) {
if (array[last] == value)
break;
last--;
}
switch (last) {
case -1:
std::cout << "Not found!";
break;
case mid:
std::cout << "Found at middle";
break;
default:
std::cout << "Found at " << last;
break;
}

If you have any questions, don't be shy :)