Thread: Windows error dealing with long

I know that, however one of my programming friends alleged that this (factoring) could be done in < 1 minute using inputs of 123456700 to 123456800. This was the best algorithm I could come up with, yet it comes nowhere close. Any better algorithms?

More craziness: When I put in 1000 to 10000, it gets all the way to 1521 and then gives me a windows error message. Any ideas?
*slams head against desk* Now when I put in, say, 12 to 22, it suddenly quits, no prompt, nothing. What is wrong?
*shoots self* My old code works with 100 to 1000, yet the "new, improved heap code" will just close. Help!

Does it help if I tell you I had to restart my machine?

No, I'm wondering why the "new (no pun intended)" code won't work with relatively small values, yet the "old" code will? This is really starting to get to me.

Just tried that Daved, and the problem remains. My old code will work, the new code, not so much.

Code:

template <typename T>
void findfactors (T n)
{
    T* arraynums = new T[n];
    for (T a = 0; a < n; a++)
    {
        arraynums[a] = 0;
    }
    arraynums[0] = 1;
    arraynums[n] = n;
    if (n == 2)
        for (T i = 3; i < n; i++)
        {
            if (n%i == 0)
                arraynums[i-1] = i;
        }
    else
        for (T i = 2; i < n; i++)
        {
            if (n%i == 0)
                arraynums[i] = i;
        }
    for (T j = 0; j < n; j++)
    {
        if (arraynums[j] != 0)
            cout << arraynums[j] << " * " << n/arraynums[j] << endl;
    }
    delete [] arraynums;
    arraynums = 0;
}

Code:

arraynums[n] = n;

no such element - memory overrun

Code:

        for (T i = 3; i < n; i++)
        {
            if (n%i == 0)
                arraynums[i-1] = i;
        }

this loop never runs

3. no need to check value more than sqrt(n)

Getting rusty on C++ (Java is in syllabus at my university), so I wrote a brute force version for practice, but I have no guarantee that it is correct. It prints the factors of each integer in the range [123456700,123456800] in about a second or less, on my computer.

I don't buy your argument about keeping your code relatively interchangeable when any C compiler will choke on your use of templates, iostreams and new[]/delete[], so I went ahead and used a std::vector.

Thanks so much, laserlight! That works perfectly.