public static Operation createOperate(string operate)
        {
            Operation oper = null;

            switch (operate)
            {
            case "+":
            {
                oper = new OperationAdd();
                break;
            }

            case "-":
            {
                oper = new OperationSub();
                break;
            }

            case "*":
            {
                oper = new OperationMul();
                break;
            }

            case "/":
            {
                oper = new OperationDiv();
                break;
            }

            case "sqr":
            {
                oper = new OperationSqr();
                break;
            }

            case "sqrt":
            {
                oper = new OperationSqrt();
                break;
            }

            case "+/-":
            {
                oper = new OperationReverse();
                break;
            }
            }

            return(oper);
        }
 public static Operation createOperate(string operate)
 {
     Operation oper = null;
     switch (operate)
     {
         case "+":
             {
                 oper = new OperationAdd();
                 break;
             }
         case "-":
             {
                 oper = new OperationSub();
                 break;
             }
         case "*":
             {
                 oper = new OperationMul();
                 break;
             }
         case "/":
             {
                 oper = new OperationDiv();
                 break;
             }
         case "sqr":
             {
                 oper = new OperationSqr();
                 break;
             }
         case "sqrt":
             {
                 oper = new OperationSqrt();
                 break;
             }
         case "+/-":
             {
                 oper = new OperationReverse();
                 break;
             }
     }
     return oper;
 }