Array of ints - does not exist in the current context

I try to make an array of ints:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
    int[] levelsSolvedCounter = new int[3];
    levelsSolvedCounter[0] = 10;
}

But I get an error:

> The name 'levelsSolvedCounter' does not exist in the current context

Although in online compiler (https://dotnetfiddle.net/) the code works just fine.

You're not allowed to write implementation on the top-level of a class. You need to define a method first.

The levelsSolvedCounter[0] = 10; is implementation. So you need to define it within a method.

You could try something like:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
	int[] levelsSolvedCounter = new int[3];

	void Update()
	{
		levelsSolvedCounter[0] = 10;
	}
}

This should work just fine:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
    int[] levelsSolvedCounter = new int[3];

    void Update()
    {           
       levelsSolvedCounter[0] = 10;
    }
}

In C#, all logic needs to be part of a method/property/etc., it cannot be directly on the class level. Only data fields and other class members can. So while int[] levelsSolvedCounter = new int[3]; is actually a valid class private data member definition, the levelSolvedCounter[0] = 10; is invalid and must be inside a method. In this case I used the Update method, which is what gets executed to update the game object state on each frame. I kept the data member outside of the method, so it is not created on each frame again and again.