Ask HN: your biggest Aha moment as a hacker?

This was a long time ago, so I don't remember the particulars, but it was in a large Fortran-based CFD flow solver code. The code used a lot of dynamically-allocated arrays, and somewhere in there we had a bug that would occasionally manifest itself in a crash. The problem of course was that we couldn't consistently reproduce it. This was before the days of really good memory debuggers, or at least, before we discovered such tools, so the bug just kind of lingered on for a long time.

The day I finally tracked it down was a red-letter day, for me personally anyways.

Learning C trying to figure out how to deal with a large 2D array (a map for an RPG) on a calculator (limited RAM and program size) when it finally clicked what a pointer is. I was hooked from that moment on.

It was my first programming assignment, actually. I was a co-op student, working in a factory. A database used to communicate between the fab area and the order/sales types, suddenly stopped working. The original author was no longer around. I have no idea why I got picked to fix it... desperation, I suppose. I vaguely remember that some poor secretary had to do everything by hand while I figured it out.

I plunged around stupidly for a long, long time. I called it a database, but really it was more like a process-- a collection of one-off tools, on a variety of machines, that slowly massaged factory data into a form useable by the front office.

Eventually I blundered my way to the solution. Reading the manual for one of the languages used, it mentioned using EBCDIC codes when writing characters. A little bell went off in my head-- somewhere I had read that another machine in the pipeline used ASCII encoding.

None of this meant anything to me, but I knew that all the programs assumed a certain line length, and defensively stuck in a line terminator character just to be certain. A little poking around revealed that, sure enough, somehow a single record of the wrong length had got into the original data file.

So in the end, changing a single character in a single program made the whole apparatus wheeze back to life.

It was a great moment for me, seeing how such a little thing could have such a huge impact. There was also a heady feeling to the fact that nobody around me seemed to have any idea what I was talking about-- they were just happy the thing finally worked again.

I am building my first web app and learning Ruby on Rails as I go, so I literally have Aha moments every single day. When I get something to work (that I've never done before) I literally jump up and down. The feeling of seeing an idea come to life is just unexplainable!