Nice-CalculatorController.cs

    [ApiController]
    [Route("calculator")]
    public class CalculatorController : Controller
    {
        // interfaces and not implementations
        private readonly IPrinter _printer;
        private readonly ICalculator _calculator;

        // "initialized" interfaces passed as controller's constructor parameters 
        public CalculatorController(IPrinter printer, ICalculator calculator) 
        {
            this._printer = printer;
            this._calculator = calculator;
        }

        [HttpGet("sum")]
        public IActionResult Sum([FromQuery] int a, [FromQuery] int b)
        {
            this._printer.PrintToConsole(this._calculator.Sum(a, b));
            return Ok();
        }
    }