static void Main(string[] args) { IntParameters x = new IntParameters(); Console.WriteLine("Please enter first number then press Enter: "); int firstNum = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("Please enter second number or leave it blank and press Enter: "); string str = Console.ReadLine(); int result; if (str == "") { result = x.MathOperation(firstNum); } else { int secondNum = Convert.ToInt32(str); result = x.MathOperation(firstNum, secondNum); } Console.WriteLine("The result of the math operation: " + result); Console.ReadLine(); }