lesson_28.cs

public int Sum(int x, int y)
{
    return x + y;
}

class Calculator
{
    public void Add(int a, int b)
    {
        int result = a + b;
        Console.WriteLine($"Result is {result}");
    }
    public void Add(int a, int b, int c)
    {
        int result = a + b + c;
        Console.WriteLine($"Result is {result}");
    }
    public int Add(int a, int b, int c, int d)
    {
        int result = a + b + c + d;
        Console.WriteLine($"Result is {result}");
        return result;
    }
    public void Add(double a, double b)
    {
        double result = a + b;
        Console.WriteLine($"Result is {result}");
    }
}

class Program
{
    static void Main(string[] args)
    {
        Calculator calc = new Calculator();
        calc.Add(1, 2); // 3
        calc.Add(1, 2, 3); // 6
        calc.Add(1, 2, 3, 4); // 10
        calc.Add(1.4, 2.5); // 3.9

        Console.ReadKey();
    }
}

void Increment(ref int val)
{
    val++;
    Console.WriteLine(val);
}

void Increment(int val)
{
    val++;
    Console.WriteLine(val);
}

int Sum(int x, int y)
{
    return x + y;
}
int Sum(int number1, int number2)
{
    return x + y;
}
void Sum(int x, int y)
{
    Console.WriteLine(x + y);
}