Why does rand() + rand() produce negative numbers?

Question

I observed that rand() library function when it is called just once within a loop, it almost always produces positive numbers.

for (i = 0; i <         


        

Answer 1

While what everyone else has said about the likely overflow could very well be the cause of the negative, even when you use unsigned integers. The real problem is actually using time/date functionality as the seed. If you have truly become familiar with this functionality you will know exactly why I say this. As what it really does is give a distance (elapsed time) since a given date/time. While the use of the date/time functionality as the seed to a rand(), is a very common practice, it really is not the best option. You should search better alternatives, as there are many theories on the topic and I could not possibly go into all of them. You add into this equation the possibility of overflow and this approach was doomed from the beginning.

Those that posted the rand()+1 are using the solution that most use in order to guarantee that they do not get a negative number. But, that approach is really not the best way either.

The best thing you can do is take the extra time to write and use proper exception handling, and only add to the rand() number if and/or when you end up with a zero result. And, to deal with negative numbers properly. The rand() functionality is not perfect, and therefore needs to be used in conjunction with exception handling to ensure that you end up with the desired result.

Taking the extra time and effort to investigate, study, and properly implement the rand() functionality is well worth the time and effort. Just my two cents. Good luck in your endeavors...