Validate an arithmetic expression programatically in c#?

Question

 

validate input like:

 

 2+1-(3*2)+8/2

 

and return its answer using MDAS rule

 

//returns 1

Answer 1

Dear  ml_coro,

 

The answer that is returned (1) is correct using the Bracktes, MDAS rules. You can verify it in

http://www.google.co.in/search?hl=en&q=2%2B1-%283*2%29%2B8%2F2&meta=

Answer 2

If you want to validate a string containing "2+1-(3*2)+8/2" in C#, you're either going to have to write a math expression parser/evaluator, or use the CodeDom support to compile the code to C# (with its syntax restrictions) and call the code directly.

Answer 3

Apart from a couple of expression evaluators:

http://www.codeplex.com/Flee
http://www.codeplex.com/LazyParser

You could also create a DataTable, add a DataColumn and exploit it's Expression property

Code Snippet

string expression = "2+1-(3*2)+8/2";

DataTable dataTable = new DataTable();
dataTable.Columns.Add("col1", typeof(int), expression);
dataTable.Rows.Add(new object[] { });
Console.WriteLine(dataTable.Rows[0][0]);

Answer 4

timvw wrote:

Apart from a couple of expression evaluators: http://www.codeplex.com/Flee http://www.codeplex.com/LazyParser You could also create a DataTable, add a DataColumn and exploit it's Expression property Code Snippet string expression = "2+1-(3*2)+8/2"; DataTable dataTable = new DataTable(); dataTable.Columns.Add("col1", typeof(int), expression); dataTable.Rows.Add(new object[] { }); Console.WriteLine(dataTable.Rows[0][0]);

 

is there a way to do this programatically?

actually, your code really worked...

Answer 5

Hi ml_coro,

       hope, this article can help you..

 

http://www.codeproject.com/KB/cpp/rpnexpressionevaluator.aspx?display=Print

 

regards,

soe moe

 

Answer 6

If you want to get really silly about this, you could use the C# compiler to dynamically compile the expression and evaluate it.

 

Here is an example way to do this; you should be able to see how you could extend this to work with other kinds of expressions. It's well over-the-top and probably grossly inefficient - but I think it could be extremely powerful:

 

Code Snippet

using System;
using System.Reflection;
using System.CodeDom.Compiler;

 

using Microsoft.CSharp;

class Program
{
    static void Main(string[] args)
    {
        TestExpression("2+1-(3*2)+8/2");
        TestExpression("1*2*3*4*5*6");
        TestExpression("Invalid expression");
    }

 

    static void TestExpression(string expression)
    {
        try
        {
            int result = EvaluateExpression(expression);
            Console.WriteLine("'" + expression + "' = " + result);
        }

 

        catch (Exception)
        {
            Console.WriteLine("Expression is invalid: '" + expression + "'");
        }
    }

 

    public static int EvaluateExpression(string expression)
    {
        string code = string.Format  // Note: Use "{{" to denote a single "{"
        (
            "public static class Func{{ public static int func(){{ return {0};}}}}",
            expression
        );

 

        CompilerResults compilerResults = CompileScript(code);

 

        if (compilerResults.Errors.HasErrors)
        {
            throw new InvalidOperationException("Expression has a syntax error.");
        }

 

        Assembly assembly = compilerResults.CompiledAssembly;
        MethodInfo method = assembly.GetType("Func").GetMethod("func");

 

        return (int)method.Invoke(null, null);
    }

 

    public static CompilerResults CompileScript(string source)
    {
        CompilerParameters parms = new CompilerParameters();

 

        parms.GenerateExecutable = false;
        parms.GenerateInMemory = true;
        parms.IncludeDebugInformation = false;

 

        CodeDomProvider compiler = CSharpCodeProvider.CreateProvider("CSharp");

        return compiler.CompileAssemblyFromSource(parms, source);
    }
}