I don't know how functions in C# work. My variable just changes the value in the function but after that it goes back to the old value. I don't know why.

static void Plus(int a, int n)
    {
        for(int i = 0; i < n; i++)
        {
            a = a + 1;
        }
    }
    static void Main(string[] args)
    {
        Console.WriteLine("a = "); 
        int a = int.Parse(Console.ReadLine());
        Console.WriteLine("n = ");
        int n = int.Parse(Console.ReadLine());
        Plus(a, n);
        Console.WriteLine($"after plus a = {a}");
    }