Heap Corruption

[stoneJax]

Hi! I have written a binary search function which finds the last occurrence of a number in an array. When I test it, it always seems to give the correct output. The problem is that a window pops up in Visual Studio saying, "Debug Error!. . . HEAP CORRUPTION DETECTED." I am assuming the problem lies in running out of bounds in the array. I have tried adjusting the bounds on the for loop and I have run the code through the debugger a bunch of times, but I cannot locate the problem.

  
#include <iostream>
using namespace std;

int maxNum, mid, number = 0, result = -1;
int* ptr = NULL;

int binarySearchFirstLastOccurance();

int main()
{
	
	cout << "How many numbers do you want to enter? ";
	cin >> maxNum;
	ptr = new int[maxNum];
	cout << "Enter values in ascending order. May use more than one occurance of the same "
		 << "number as long as they are consequative." << endl;
	
	
	for(int count = 0; count < maxNum; count++) {
		 
		ptr[count] = 0;
	}

	for (int count = 1; count <= maxNum; count++) {
		cin >> ptr[count]; 
		
	}
	for (int count = 1; count <= maxNum; count++) {
		cout << ptr[count] << " ";
	}

	cout << "\nWhat number do you want to search for? ";
	cin >> number;
	
	if (binarySearchFirstLastOccurance() > 0)
		cout << "\nThe last occurance of this value is located in the number " << result << " element." << endl;

	else cout << "\nThat number is not in the array." << endl;
	
	delete[] ptr;
	
	return 0;

}





int binarySearchFirstLastOccurance( )
{
	int left = 1, right = maxNum;

	while (left <= right) {

		mid = (left + right) / 2;
		if (number == ptr[mid]) {
			result = mid;
			left = mid + 1;
		}
		else if (number < ptr[mid])
			right = mid - 1;

		else left = mid + 1;
	}
	return result;
}

[salem c]

> for (int count = 1; count <= maxNum; count++)
This is wrong.

> for(int count = 0; count < maxNum; count++)
This is right.

> ptr = new int[maxNum];
Subscripts start at 0 and end at maxNum - 1
By starting at 1, and ending with <=, you step off the end.

> cin >> number;
> if (binarySearchFirstLastOccurance() > 0)
Mmm, now try it using parameters instead of a rats nest of global variables.

[dutch]

How exactly is your binary search going to find the last matching value? Think about it. What if the array contains 5, 5, 5, 5, 5 and you search for 5?

BTW, it's spelled "occurrence".

[stoneJax]

@salem
I had tried that earlier too, but then I wasn't getting the correct output. However, I adjusted my for loops back like you mentioned, just you saying that was enough to steer me in the direction of looking at my algorithm closer. I adjusted my result variable to result = mid + 1 and it seems to be working now.

I actually intend to use parameters, but just wanted to make sure I had the algorithm working correctly first.

@ Dutch
it works with your example now too.

Thanks!