Counter of Digits in C #

You could transform your number into string to get the number of digits, go through them and check whether or not they are even

string numeroString = dato.ToString();
int numerosPares = 0;
for (int i = 0; i < numeroString.Length; i++)
{
    if ((int.Parse(numeroString[i].ToString()) % 2) == 0)
    {
        numerosPares++;
    }
}
Console.WriteLine("Total numeros pares: "+ numerosPares);

To check if a number is, or not even, it is best to use check if, by dividing by 2, its remainder is 0, in essence, if the condition num % 2 == 0 implies that num is even, then, there are lots of possibilities to do what you are looking for, one could be using foreach

static int contarParesConForeach(int d)
{
    int cont = 0;
    foreach(char c in d.ToString())
    {
        if (Convert.ToInt16(c) % 2 == 0)
        {
            cont++;
        }
    }
    return cont;
}

Another could be using Linq with Where and Count

static int contarParesCount(int d) => d.ToString().Where(x => x % 2 == 0).Count();

Both functions will produce exactly the same result

Console.WriteLine($"{contarParesConForeach(623)}");
//Output: 2
Console.WriteLine($"{contarParesCount(623)}");
//Output: 2

A page where you will find methods in C # .... I have the solution to your problem, I would recommend, if you are going to use them in a button, put this method of bass, not within the action of the button: