Program not exiting because of delete[] - c++

Question

So my program executes as expected and prints out the correct result. The only issue is that after it is done it does not exit. If I wait a few more seconds windows pops up an error message saying "bignumbs.exe has stopped working". Here is the code to the new function which seems to be causing the problem.
void BigInt::u_basic_mult(const BigInt& n, int digs)
{
const base_int* tptr = n.used > used ? n.data : data;
const base_int* bptr = tptr == data ? n.data : data;
const int tlen = tptr == data ? used : n.used;
const int blen = bptr == data ? used : n.used;
if(digs < 1)
digs = tlen + blen + 1;
base_int* new_data = new base_int[digs];
for(int i = 0; i < digs; ++i)
*new_data++ = 0;
for(int i = 0; i < blen; ++i)
{
int stop_pt = MIN(tlen, digs - i);
overflow_int carry = 0;
overflow_int btmp = bptr[i];
for(int j = 0; j < stop_pt; ++j)
{
overflow_int prod = btmp * tptr[j] + carry;
carry = prod >> BASE_BITS;
overflow_int sum = new_data[i + j] + carry + (prod & MAX_DIG);
carry += sum >> BASE_BITS;
new_data[i + j] = sum;
}
}
//delete[] data; these two lines cause the error
//data = new_data;
used = digs;
alloc = digs;
strip_zeros();
}
Notice the two lines I commented out. Without them the program executes and finishes (although now the result is incorrect). What is it about changing the value of a pointer or deleting it which could make my program have this strange error? Also I am pretty sure data is valid since I use it in the code above.
Also I am compiling with G++ through Netbeans.
After inspecting further it seems that the problem may be with my deconstructor. If I comment out the delete[] data in the deconstructor the error seems to go away. I don't know why.
BigInt::~BigInt()
{
if(data) delete[] data;
}

Answer 1

for(int i = 0; i < digs; ++i)
*new_data++ = 0;
This code is modifying where the new_data pointer is pointing at, so that it is no longer pointing at the original array when you enter the subsequent loop, or do anything with it for that matter. The pointer you pass to delete[] must be pointing at the same memory address that new[] returned.
The correct way to zero-initialize the array is to do this instead:
for(int i = 0; i < digs; ++i)
new_data[i] = 0;
Or, get rid of the loop and just use memset() instead:
memset(new_data, 0, digs * sizeof(base_int));

Answer 2

You must be very careful about matching up uses of new and delete. If you allocate something using the array form of new, you must delete it using the array form of delete. If you mix-and-match the array and non-array forms, you'll get crashes like this. You also must never delete something that wasn't allocated with new, and you must never delete the same thing twice.
I can't give you any more specific advice about this particular program, because you do not show us where the pointer named data is allocated.

Answer 3

I got it. I managed to screw up my new_data pointer.
for(int i = 0; i < digs; ++i)
*new_data++ = 0;
I changed it to this.
for(int i = 0; i < digs; ++i)
new_data[i] = 0;