###This is an expression calculator which enables the users to naturally input expressions and define variables and functions.

• Author : Jingping Yu

Features

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• Easy-plugin
• Supports handling with wrong expressions and generate corresponding warnings
• Supports user-defined functions and variables

Documentation

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• From now on I will update the document in the online project and make sure it bounds with the codes. Currently you may refer to the docs bellow or have a glance at the codes.

####Setup and Installation

• Currently the project is still ongoing and due to the fact that I have never planned to make it a fully functional library (It is a homework only actually) the structure is in chaos. However, all you need to do is to #include "ExpressionParser.hpp" in your own project.

####Create an Expression

• In order to work as an expression calculator, an expression is definitely required. You may Create an expression by Expression *expression = new Expression ("5 * x + 7 x sin (SHIT (1, 11.24 ^ x))");

####Create a parser

• With your expression defined, you may create a parser by ExpressionParser *parser = new ExpressionParser (expression);

####Define variables

• As you can see there is an 'x' variable in the expression above. In order to make the parser know this, you need to call the method like this : parser->SetVariable ("x", 1.1);.

####Define Functions

• There is a "SHIT" function left undefined in the expression above. There is an AddNewFunction method in the ExpressionParser Class with three parameters : string func_name, int var_num, string expression. And you may define the function like this: parser->AddNewFunction ("SHIT", 2, "max (a + b) * sin (a / b)");.

####Calculating Results

• Now that you have given an expression and defined the variables and functions, the parser is ready to work now! Simply call parser->ParseExpression (); and the result would be stored in the parser. In order to get the result, please call Calculation *result = parser->GetResult ();. Please note that you are not getting a double value but rather a Calculation Result. There are three elements stored in a CalculationResult:

• Numeric : The actual result of the operation.
• IsValid : Is the operation actually valid.
• StatusInformation : The concise information about the operation. Whether the operations are manipulated well or some problems encountered.

• Since now the Expression Calculator must store Double, Matrix and Array as its result, all these value types inherit from a class called as Numeric. Meanwhile in order to make sure that memory leak is avoided, numeric is stored in a shared_ptr. Hence, in order to get the result, you may simply code like this: Numeric *res = parser->ParseExpression ().numeric.get ();
• After that, you can cast your Numeric * to other types by using staic_cast or dynamic_cast depending on the situation. If you are not sure what exactly is stored in the result, you may use res->GetType () == NumericType :: (COMPARE_TYPE) to check. Once you are pretty sure about what is stored, static_cast is encouraged to use since it is approximately three times faster than dynamic_cast.

##Releasing Notes

• Now the expression calculator and the numerical analyzer is pretty functional. However the document is still ongoing. I will continue on documenting to make sure that all the users could get the first-hand doc at any time for use.
• GL & HF!