static void Main(string[] args)
{
ArifmeticOperation arifmeticOperation = (a, b, c) => (a + b + c) / 3;
Console.WriteLine("result {0:f2}", arifmeticOperation?.Invoke(2, 3, 5));
Console.ReadLine();
}
static void Main(string[] args)
{
Console.WriteLine("Введите арифметическую операцию с 2 членами");
string inputData = Console.ReadLine();
Regex regexNumbers = new Regex(@"\d+");
Regex symbol = new Regex(@"\+|-|\*|\/");
int fistNumber = Convert.ToInt32(regexNumbers.Matches(inputData)[0].Value);
int secondNumber = Convert.ToInt32(regexNumbers.Matches(inputData)[1].Value);
string arifmeticSymbol = symbol.Match(inputData).Value;
ArifmeticOperation ao = null;
InitialDelegate(arifmeticSymbol, ref ao);
Console.WriteLine(ao.Invoke(fistNumber, secondNumber));
Console.ReadKey();
}