public string Calculator(string opration) { try { _operation.InterpretInput(opration); switch (Operands_Singleton.Instance.currentOperator) { case "a": _operation = new Add(); break; case "s": _operation = new Subtraction(); break; case "d": _operation = new Division(); break; case "m": _operation = new Multiplication(); break; default: break; } _operation.op1 = Operands_Singleton.Instance.operand1; _operation.op2 = Operands_Singleton.Instance.operand2; var res = _operation.CalculateResult().ToString(); return(res); } catch (Exception ex) { return(""); } }