Binary Search algorithm c++ - c++

Question

I'm trying to write a function which takes an array of integers & searches the part of the array between the first and last for the given value. If the value is in the array, return that position. If it is not, I want to return -1.
Here is the code for my function.
int binarySearch(int *array, int min, int max, int value) {
int guess = 0;
bool found = false;
while (!found) {
guess = ((array[min] + array[max]) / 2);
if (array[guess] == value) {
found = true;
return guess;
}
else if (array[guess] < value) {
min = guess + 1;
}
else if (array[guess] > value) {
max = guess - 1;
}
}
return -1;
}
I'm unsure how to break out of the while loop when the value you are searching for is not in the array? This is the pseudocode I am following for implementing a binary search function :
Let min = 0 and max = n-1(array size -1 ). Compute guess as the average of max and
min, rounded down (so that it is an integer).
If array[guess] equals
target, then stop. You found it! Return guess.
If the guess was too
low, that is, array[guess] < target, then set min = guess + 1.
Otherwise, the guess was too high. Set max = guess - 1.
Go back to step 2.

Answer 1

I think it makes sense to change what the function returns. Instead of returning guess, it should return a valid index if the item is found and -1 otherwise.
Also, you are using guess as a value and as an index. That will definitely cause problems.
guess is a value below.
guess = ((array[min] + array[max]) / 2);
guess is an index below.
else if (array[guess] < value) {
Here's my suggestion:
// Return the index if found, -1 otherwise.
int binarySearch(int *array, int first, int last, int value)
{
// Terminating condition 1.
// If first crosses last, the item was not found.
// Return -1.
if ( first > last )
{
return -1;
}
int mid = (first + last)*0.5;
// Terminating condition 2.
// The item was found. Return the index.
if ( array[mid] == value )
{
return mid;
}
// Recurse
if (array[mid] < value)
{
return binarySearch(array, mid+1, last, value);
}
else
{
return binarySearch(array, first, mid-1, value);
}
}

Answer 2

No need for recursion if you use a while loop, just remember to calculate guess every time, and set guess to the middle of the indexes, not their values:
int binarySearch (int *array, int first, int last, int value)
{
int guess = 0;
while (first != last || array[guess] == value) {
guess = (first + last) / 2;
if (array[guess] == value)
return guess;
else if (array[guess] < value)
last = guess + 1;
else if (array[guess] > value)
first = guess - 1;
}
return -1;
}
I would also suggest
int first = 0, last = sizeof(array) / sizeof(array[0]) - 1;
instead of passing them as arguments.