Random.Range confuses me..

I have a simple script to make a character walk to a random waypoint in a list.

NextWaypoints is a list, that can have either 0, 1 or 2 values, which is the same as NextWaypoints.Count if I'm not mistaken. If NextWaypoints.Count it's 2, it should pick one of the two. So either 0 (first item) or 1 (second item).

However the code below always sets random to 0.

Code (CSharp):

1. if (NextWaypoints.Count>0) {
2. int random = Random.Range(0, NextWaypoints.Count - 1);
3. print(random + " / " + NextWaypoints.Count + "(Random between 0 and " + (NextWaypoints.Count - 1));
4. currentWaypoint = NextWaypoints[random];

The only way I can fix it, is to change this line to:

Code (CSharp):

1. int random = Random.Range(0, NextWaypoints.Count);

But this confuses me. Shouldn't that return a value between 0-2, so 0, 1 or 2?

When I just use print(Random.Range(0,1) it works and returns 0 or 1. Why doesn't it when I use the Count from a list?

 

I'm not sure but you might be bumping up against the difference between Random.Range with a float or with an integer. One has an inclusive max value, the other an exclusive max value. In other words, if you use integers, the last value won't be chosen. Check it out here:
https://docs.unity3d.com/ScriptReference/Random.Range.html

I actually complained about it on one of these forums because it took me quite a while to debug what was going wrong with a program. It's inconsistent, and the worst is, they tell you about the integers second, so I just assumed integers were inclusive for max value. One of those times my skimming got me in trouble.

 

It doesn't; it only returns 0. System.Random works like that also (it's fairly common for random integer ranges to be upper bound exclusive).

--Eric

 

In unity Random.range does not return the top value you set into it if it's a list or array call (since their initial reference value is 0 rather than 1) for ease of putting in list.count and array.legnth calls. Therefore remove your count-1 and set as just count then you should be in buisness!

 

Allright, thanks for clearing that out for me. Seems to have missed that in the docs. I tried (int) to force it to use the int version, but apparently that wasn't the issue