Styjun

I urge caution against choosing an existing generic expression evaluator over a purpose-built math evaluator. The reason for this is that the expression evaluators are not limited to just math. A clever individual could use this to create an instance of any type in the framework and call any method on the type, and that would allow him to do some decidedly unwelcome things. For example: new System.Net.WebClient().DownloadFile("illegalchildpornurl", "C:openme.gif") will evaluate just fine in most of those, and do just what it sounds like it would (and make you a felon at the same time).

This doesn't mean don't look for something that's already written. It just means be careful. You want one that does math, and only math. Most of what's already out there isn't that picky.

I was recently using mXparser, which is a math parser library. It gives you a lot of flexibility, such as variables, functions, constants, operators. You will find below a few usage examples:

Example 1 - simple formula

Expression e = new Expression("1 + pi");
double v = e.calculate();

Example 2 - formula with variables, functions, etc.

Argument x = new Argument("x = 2");
Constant a = new Constant("a = sin(10)");
Function f = new Function("f(t) = t^2");
Expression e = new Expression("2*x + a - f(10)", x, a, f);
double v = e.calculate();

https://mxparser.codeplex.com/

http://mathparser.org/

Found recntly - you can try the syntax (and see the use case) via the Scalar Calculator app that is powered by mXparser.

Best regards

Best regards

I would also have a look at Jace (https://github.com/pieterderycke/Jace). Jace is a high performance math parser and calculation engine that supports all the .NET flavors (.NET 4.x, Windows Phone, Windows Store, ...). Jace is also available through NuGet: https://www.nuget.org/packages/Jace

Here is one way to do it. This code is written in Java. Note it does not handle negative numbers right now, but you can add that.

public class ExpressionParser 
public double eval(String exp, Map<String, Double> vars)
 int bracketCounter = 0;
 int operatorIndex = -1;

 for(int i=0; i<exp.length(); i++)
 if(operatorIndex < 0)
 exp = exp.trim();
 if(exp.charAt(0) == '(' && exp.charAt(exp.length()-1) == ')')
 return eval(exp.substring(1, exp.length()-1), vars);
 else if(vars.containsKey(exp))
 return vars.get(exp);
 else
 return Double.parseDouble(exp);
 
 else
 switch(exp.charAt(operatorIndex))
 case '+':
 return eval(exp.substring(0, operatorIndex), vars) + eval(exp.substring(operatorIndex+1), vars);
 case '-':
 return eval(exp.substring(0, operatorIndex), vars) - eval(exp.substring(operatorIndex+1), vars);
 case '*':
 return eval(exp.substring(0, operatorIndex), vars) * eval(exp.substring(operatorIndex+1), vars);
 case '/':
 return eval(exp.substring(0, operatorIndex), vars) / eval(exp.substring(operatorIndex+1), vars);
 
 
 return 0;

You need to import java.util.Map.

Here is how I use this code:

 ExpressionParser p = new ExpressionParser();
 Map vars = new HashMap<String, Double>();
 vars.put("x", 2.50);
 System.out.println(p.eval(" 5 + 6 * x - 1", vars));

Another option you may want to look into is the Spring.NET Framework's expression evaluation functionality. It can do a lot more than math, too.

However, the entire Spring.NET Framework might be a bit of overkill for your needs if you don't require the rest of the functionality.

Related: Equation expression parser with precedence.

As I answered in this thread (Best Free C# Math Parser using variables, user defined functions, custom operators), you can use Mathos Parser, which you can simply paste into your source code.

 Mathos.Parser.MathParser parser = new Mathos.Parser.MathParser();

 string expr = "(x+(2*x)/(1-x))"; // the expression

 decimal result = 0; // the storage of the result

 parser.LocalVariables.Add("x", 41); // 41 is the value of x

 result = parser.Parse(expr); // parsing

 Console.WriteLine(result); // 38.95

I recomend you to use MEEL for this.

// parse string to IExpression (symbolic type)
IExpression expression = BaseExpression.Parse("(x+(2*x)/(1-x))");

// create your own collection for attributes
var attributes = new MathAttributeCollection();
// create local variable named "x" with value 5
var attributeX = new ScalarAttrInt("x") Value = new ScalarConstInt(5);
attributes.Add(attributeX);

// execute math expression where x=5
var result = expression.Execute(attributes);

MessageBox.Show(result.GetText());
// result: 2.5