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String Parser and Evaluator

, 7 Apr 2003
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Formula parser for C#

Sample Image - String_Evaluator.gif

Introduction

This formula evaluator can use different data types like int, double, string, DateTime or bool to calculate the value of a mathematical expression. You can use any of the operators, +, -, *, /, >, <, == etc., and specify parameters for them.

Background

.NET doesn't support types like Variant as in VB6 or Delphi. To avoid validating data type before doing any operation, I could create Variant type that can be used to save data of different types and overload some operators that are frequently used, like bitwise +, unary + -, *,/.

This code works in 2 steps: First, parse the expression and transform it to Backward Poland Notation. Now every order item can be either an operator or an operand. Second, calculate value of order using stack. Variables are saved in a public static field, that has the Hashtable type shown in the "string/value" view.

Using the code

To use this code, you must add a reference to the Evaluator.dll library.

Hashtable ht = new Hashtable();
ht.Add("A",12);
ht.Add("B",15);
Za.Evaluator.Evaluator.Variables = ht;
try
{
    textBox1.Text = Za.Evaluator.Evaluator.Evaluate("[A] + [B]/1.2").ToString();
}
catch(Za.Evaluator.CalcException ex)
{
    SomeCode xxxxxxxxx;
}
catch(Exception ex)
{
    SomeCode xxxxxxxxx;
}            

To realize addition functions, you need to edit EmbeddedFunction in Calculator.cs file.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Zainaustria
Web Developer
Russian Federation Russian Federation
No Biography provided

Comments and Discussions

 
GeneralOperator Or (and,...) Pinmemberrichardlukes12-Nov-08 0:49 
GeneralUpdated Code Pinmemberzacksz26-Sep-08 11:03 
GeneralMuch easier to do this in .NET 2.0 PinmemberKristopher Cargile8-Apr-08 14:04 
GeneralA Bug needs attention Pinmembersakykhan30-May-07 14:04 
(10/1.5)-2
 
gives 8.667
which should be 4.667
 
On division with a floating point value, it treats the - as + .
 
Any patch for this?
 

 
Fix before the nuclear reactors blow up!
GeneralMinus/Substract Bug resolved PinmemberAfersol003-Aug-06 9:47 
GeneralGood Work, but got a bug PinmemberMarais13-Mar-06 20:46 
Generalbug Pinmemberwanwenguo20-Jan-05 20:42 
Generalbuggy Pinmemberdl4gbe21-Dec-04 16:12 
GeneralRe: buggy Pinmemberpatmarleon2-Jul-11 11:34 
GeneralI'd like to submit some improvements PinmemberMike9513-Feb-04 5:44 
GeneralRe: I'd like to submit some improvements PinmemberTony M John27-Feb-04 4:24 
GeneralRe: I'd like to submit some improvements Pinmemberemiliodabdoub25-Sep-07 21:12 
GeneralImprovements PinmemberMatthew Dye28-Nov-03 6:51 
GeneralWhy not CodeDOM PinmemberJonathan de Halleux9-Oct-03 4:33 
GeneralBug PinmemberChibacity9-Oct-03 4:28 
GeneralRe: Bug PinmemberTJ Manjaly1-Mar-04 7:30 
GeneralRe: Bug PinmemberNaues16-Aug-04 4:43 
GeneralRe: Bug PinmemberSerkan Kokturk20-Dec-06 3:16 
GeneralAnd &amp;&amp; Or operators PinmemberJ.M.Piulachs13-Sep-03 22:00 
QuestionUsage guidelines? PinsussArchieBunker22-May-03 10:57 
GeneralNicely Done PinmemberBlake Coverett8-Apr-03 18:07 
GeneralRe: Nicely Done Pinmemberjdunlap1-Sep-03 12:50 
GeneralRe: Nicely Done Pinmemberemiliodabdoub25-Sep-07 21:13 

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