Persistent variable for all list members inside a loop called every frame

Question

I'm trying to add a sort of manager to handle all objects in a list and increase a float value that each individual member of the list has given a condition every single frame. I'm having some trouble wrapping my head around the actual code I need though.

So say I've got an OverlapCircleAll or trigger checking for tagged objects in a certain radius. These objects are then added to a List (foo).

Then, I go through foo with a for loop and declare a float value x for each object.

What I need is for each object's x to increase when the object is also on another list, bar.

So something like this:

for (int i = 0; i < foo.Count; i++)
{
     float x;
     //or float x = 0;?

     if (bar.Contains(foo[i]))
     {
          x += 1f;
     }
}

The problem is, I can't figure out how to make the value of x persist each loop. This function is called in Update() so the idea is that the longer an object is in both foo and bar, the higher its value of x is. I don't know how to save the value of x for the next loop though. Ideally something like:

for (int i = 0; i < foo.Count; i++)
{
     float x;

     if (lastX != null)
     {
          x = lastX;
     }
     else
     {
          x = 0;
     }

     if (bar.Contains(foo[i]))
     {
          x += 1f;
     }

     float lastX = x;
}

But I don't know a) how to save lastX for each object in the list and b) set x to lastX (because for each loop it creates a lastX).

I thought about storing each x in an array of floats and calling the corresponding array[i] to foo[i] to get x, but if I remove something from the list then the array will become desynchronised with the list and all the x values will get muddled up.

What is the correct way to go about this?

schneebuzz · Accepted Answer · 2020-04-24 08:23:35Z

The correct way is very different at times.

Change variable scope

In the first part of the code you use float x; inside the for loop. This means x is in the scope of the for loop block, it is recreated every loop.

You can change the scope by declaring x outside of the loop, then it is recreated each (assumed) Update call. Since you would want x to persist between calls to Update you need to move it outside of it (change scope). This makes x a class variable (there are different names for that too) and looks like this:

public class Example : MonoBehaviour
{
    private float x = 0f;

    void Update()
    {
        for(...) {...}
    }
}

Keeping values where they belong to

Your second problem is a different story. For each element in your list you need a value x bounded to that element. This strongly suggests that x is part of that element. A good way to solve this is to add the float x to whatever type your elements are. If the elements are objects of one of your own classes, you can just add a new variable x to this class. Then access it using

foo[i].x

If the elements are objects of built in unity classes you can create a Wrapper class along the lines of:

public class MyElements
{
    public float x;
    public GameObject originalElement; // assumption...
}

Then when filling your list/array you fill it with MyElements.

All in all this is a basic C#/programming problem which is not related to game development. You can learn how to do this in various tutorials/books or other resources. If you need assistance, update your question or post a new one (preferrably on a suitable stackexchange site).

Final note

As you realized, it is difficult to properly handle a parallel list of x. No question it can be done but it is very error prone.

Thanks a ton, this helped a lot. I made a wrapper class and everything's working exactly how I want it to. Thanks for the in-depth response! I realise now I probably should have put this on StackOverflow or something, my bad ahaha — Cube ok
– Cube ok, Commented Apr 26, 2020 at 6:48

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Persistent variable for all list members inside a loop called every frame

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Change variable scope

Keeping values where they belong to

Final note

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Persistent variable for all list members inside a loop called every frame

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Change variable scope

Keeping values where they belong to

Final note

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