To a large extent, we understand how to write bug-free programs andcode: you use and test the program until it doesn't crash or breakthings, produces the correct results, and doesn't do anything surprising(generate extra messages, pop up stray windows, and so on). There arevarious different ways to do this and people disagree about whichapproach is the most effective, but this is the broad view of how mostbug-free program development is done.

('bug-

Around here, our systems have layers of accreted history; scriptsthat are generating files that are used by, well, we're sometimes notentirely sure any more. Every so often we reach the point where we turnanother one of the file-generating scripts off (we take them out ofcrontabs, we remove invocations of them from other scripts and so on).

Having done this for a while now, I have a suggestion: when a data filebecomes obsolete and is no longer updated, you should

Here's an interesting and fun bug (in C) that I once ran across, yearsago. Suppose that you have a hash table, with entries chained off eachother in case of a hash collision, and a function to remove an elementfrom it that looks like this:

void remove(elem *mp){  elem *np;  np = table[HASH(mp)];  if (np == mp) {    table[HASH(mp)] = mp->next;    return