You should take the following two steps when applying USPExpress Pro to an expression:

• Parse the expression
  
  • Parsing results in producing an expression tree. Once the tree is built, the expression can be evaluated many times against various variable values.
• Evaluate the expression
  
  • Since the expression tree is already built, evaluation of the expression is performed with maximum possible speed - no additional overhead is involved.

Below is a step-by-step guide to USPExpress usage (in C# syntax):

1. Declare and create USP.Express.Pro.Parser object:
   
   

   using USP.Express.Pro;
   ...
   Parser m_cParser = new Parser();
   

2. Specify variables which you intend to use in your expression. Four variables named X1, X2, X3, X4 are specified in the example below:
   
   

   m_cParser.Variables.Add(new Variable("x1", typeof(Double)));
   m_cParser.Variables.Add(new Variable("x2", typeof(DateTime)));
   m_cParser.Variables.Add(new Variable("x3", typeof(String)));
   m_cParser.Variables.Add(new Variable("x4", typeof(Boolean)));
   

   Optionally, you may add aliases to your variables. Each variable can have one or more aliases:

   m_cParser.Variables.Item(2).Aliases.Add("OrderDate");
   

3. Parse the expression and obtain an expression tree:
   
   

   ExpressionTree m_oExpressionTree = null;
   try
   {
     m_oExpressionTree = m_cParser.Parse("Your Expression");
   }
   catch(Exceptions.ParseException ex)
   {
     ...
   }
   catch(Exception ex)
   {
     ...
   }  
   

   ParseException is raised, if the expression is not parsed successfully.
   
4. Assign actual values to the variables that you specified on step 2:
   
   

   object[] m_aValues = new object[4];
   
   m_aValues[0] = 1.0;
   m_aValues[1] = DateTime.Now;
   m_aValues[2] = "test string";
   m_aValues[3] = true;
   

5. Evaluate the expression:
   
   

   string sResult;
   
   try
   {
      sResult = m_oExpressionTree.Evaluate(m_aValues).ToString();
   }
   catch(Exceptions.EvaluateException ex)
   {
      MessageBox.Show(ex.Message);
   }
   catch(Exception ex)
   {
      MessageBox.Show(ex.Message);
   }
      
   

   EvaluateException is raised, if the expression is not evaluated successfully.
   

You may also refer to the Sample projects and the Class Reference document that comes with the library.