public static Operation CreateOperation(string oper)
 {
     Operation operation = null;
     switch (oper)
     {
         case "+":
             operation = new OperationAdd();
             break;
         case "-":
             operation = new OperationSub();
             break;
         case "*":
             operation = new OperationMul();
             break;
         case "/":
             operation = new OperationDiv();
             break;
     }
     return operation;
 }
        public static Operation CreateOperation(string oper)
        {
            Operation operation = null;

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

            case "-":
                operation = new OperationSub();
                break;

            case "*":
                operation = new OperationMul();
                break;

            case "/":
                operation = new OperationDiv();
                break;
            }
            return(operation);
        }