Interface of expression calculator.

You can find more information in comments below.

class ICalculator
    {
    public:
        virtual int getErrorCount() = 0; // Return error count 
        virtual ERROR_INFO getError(const int index) = 0; // Return error info by index 
        virtual int getProcedureCount() const = 0; // Return assigned procedure count 
        virtual IProcedure *getProcedure(const int index) = 0; // Return procedure by index 
        virtual IProcedure *getProcedure(const String &name) = 0; // Return procedure by name 
        virtual int getVariableCount() const = 0; // Return assigned variable count 
        virtual CVariable *getVariable(const int index) = 0; // Return variable by index 
        virtual CVariable *getVariable(const String &name) = 0; // Return variable by name 
        virtual IEntityCalculator *getEntityCalculator() = 0; // Return assigned or default entity calculator 
    
        virtual bool setEntityCalculator(IEntityCalculator *value) = 0; // Set new entity calculator. Old one will be destroyed. If nullptr is passed, default one will be used 
    
        virtual bool AddProcedure(IProcedure *proc) = 0; // Add procedure 
        virtual bool DeleteProcedure(const int index) = 0; // Delete procedure by index 
        virtual bool DeleteProcedure(IProcedure *proc) = 0; // Delete specified procedure 
        virtual bool DeleteProcedure(const String &name) = 0; // Delete procedure by name 
        virtual bool ClearProcedures() = 0; // Delete all procedures 
    
        virtual bool AddVariable(CVariable *value) = 0; // Add variable 
        virtual CVariable *AddVariable(const String &name) = 0; // Create and add variable with specified name 
        virtual CVariable *AddVariable(const String &name, const String &value) = 0; // Create and add variable with specified name and string value 
        virtual CVariable *AddVariable(const String &name, const long long value) = 0; // Create and add variable with specified name and integer value 
        virtual CVariable *AddVariable(const String &name, const double value) = 0; // Create and add variable with specified name and float value 
        virtual void SetVariable(const String &name, const String &value) = 0; // Create or update variable with specified name to new specified string value 
        virtual void SetVariable(const String &name, const long long value) = 0; // Create or update variable with specified name to new specified integer value 
        virtual void SetVariable(const String &name, const double value) = 0; // Create or update variable with specified name to new specified float value 
        virtual bool DeleteVariable(const int index) = 0; // Delete variable by index 
        virtual bool DeleteVariable(CVariable *item) = 0; // Delete specified variable 
        virtual bool DeleteVariable(const String &name) = 0; // Delete variable by name 
        virtual bool ClearVariables() = 0; // Delete all variables 
    
        virtual void ClearErrors() = 0; // Clear previous calculation errors 
        virtual CVariable *Calculate(CExpression *expression, CVariable *parent) = 0; // Calculate expression 
        virtual void Release() = 0; // Delete itself 
    };