String calculator

Question

Hi fellow programmers,

I am creating a calculator in C#

and I have a string variable math which contains 100 * 5 - 2

How can I display its output which is 498 in my console?

My code is this:

String math = "100 * 5 - 2"; 

Console.WriteLine(math);

Console.ReadLine(); // For Pause

So basically, what my code will give me is the string itself which 100 * 5 - 2

but I want it to give me 498 as a result.

Idea about this is pretty much appreciated.

Thanks

Please search for "C# parse math expression" and make you question more concrete. If you don't know how to use search engines here is starting point http://stackoverflow.com/questions/234217/is-it-possible-to-compile-and-execute-new-code-at-runtime-in-net for parsing options. — Alexei Levenkov, Feb 22 '14 at 05:22
Dijkstra's Shunting Yard algorithm may be of interest to you: http://en.wikipedia.org/wiki/Shunting-yard_algorithm — pcnThird, Feb 22 '14 at 05:24
possible duplicate of [evaluate an arithmetic expression stored in a string (C#)](http://stackoverflow.com/questions/4620437/evaluate-an-arithmetic-expression-stored-in-a-string-c) — Anderson Green, Feb 22 '14 at 05:49

score 19 · Accepted Answer · edited Aug 20 '18 at 16:26

19

Regular Expression evaluation can be done using DataTable.Compute method (from MSDN) :

Computes the given expression on the current rows that pass the filter criteria.

Try this:

using System.Data;//import this namespace

 string math = "100 * 5 - 2";
 string value = new DataTable().Compute(math, null).ToString();

edited Aug 20 '18 at 16:26

Antoine

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answered Feb 22 '14 at 05:50

Sudhakar Tillapudi

24,787
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yes.. i just saw it. Perfect! – GM-Xile GM-Xile Feb 22 '14 at 05:55
Is it correctly working? – Ramesh Rajendran Feb 22 '14 at 05:59
Just keep in mind that `DataTable.Compute()` does not work on mono (probably because of some mono implementation bug). – plunntic iam Nov 17 '15 at 11:24

score 2 · Answer 2 · edited May 23 '17 at 12:10

2

Simply try this

String math = (100 * 5 - 2).ToString();

I don't know, Why you want more complex? It's very easy ..

And if you want surely that,You can do that by using EvaluateExpression

public int EvaluateExpression(string math )
    {
       return Convert.ToInt32(math);
    }

........................

String math = "100 * 5 - 2"; 

int result = EvaluateExpression(math );

Console.WriteLine(result );

See this discussions

Evaluating string "3*(4+2)" yield int 18

Update:

If those values came from input textbox, then write this way

String math = txtCalculator.Text.Trim();

    int result = EvaluateExpression(math );

    Console.WriteLine(result );

And also you can find out some pretty answer from this discussion

Is it possible to compile and execute new code at runtime in .NET?

Update 2:

Finally I have tried this sample for you :

My full code for class library

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Xml.XPath;

public partial class _Default : Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        String math = "100 * 5 - 2";

        Console.WriteLine(Evaluate(math));
    }

    public static double Evaluate(string expression)
    {
        var xsltExpression =
            string.Format("number({0})",
                new Regex(@"([\+\-\*])").Replace(expression, " ${1} ")
                                        .Replace("/", " div ")
                                        .Replace("%", " mod "));

        // ReSharper disable PossibleNullReferenceException
        return (double)new XPathDocument
            (new StringReader("<r/>"))
                .CreateNavigator()
                .Evaluate(xsltExpression);
        // ReSharper restore PossibleNullReferenceException
    }
}

edited May 23 '17 at 12:10

Community

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answered Feb 22 '14 at 05:26

Ramesh Rajendran

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I guess the OP wanted to also evaluate user input – pcnThird Feb 22 '14 at 05:27
@pcnThird , Also yes, But the OP did't mention that. – Ramesh Rajendran Feb 22 '14 at 05:28
Hi sir, What if the value comes from a textbox which is basically a string, right? – GM-Xile GM-Xile Feb 22 '14 at 05:30
@GM-XileGM-Xile: you mean the string `"100 * 5 - 2"` comes from textbox? right? – Sudhakar Tillapudi Feb 22 '14 at 05:32
@SudhakarTillapudi Yes sir – GM-Xile GM-Xile Feb 22 '14 at 05:33
@GM-XileGM-Xile - I have change my answer. Please take a look at that – Ramesh Rajendran Feb 22 '14 at 05:33
@RameshRajendran: what is `EvaluateExpression` there in your code? – Sudhakar Tillapudi Feb 22 '14 at 05:35
That means : String math = (100 * 5 - 2).ToString(); – Ramesh Rajendran Feb 22 '14 at 05:36
@RameshRajendran: are you sure that works? – Sudhakar Tillapudi Feb 22 '14 at 05:37
1

The name EvaluateExpression does not exist in the current context. – GM-Xile GM-Xile Feb 22 '14 at 05:37
@GM-XileGM-Xile - See my updated answer – Ramesh Rajendran Feb 22 '14 at 05:39
@RameshRajendran: do you think `100*5 -2` can be converted into integer? – Sudhakar Tillapudi Feb 22 '14 at 05:41
Input string was not in a correct format. – GM-Xile GM-Xile Feb 22 '14 at 05:42
@GM-XileGM-Xile . May be your text box have any spaces, So you got the problem, You can use Trim() – Ramesh Rajendran Feb 22 '14 at 05:44
Still the same. I removed the spaces already yet the error still occurs. – GM-Xile GM-Xile Feb 22 '14 at 05:46
@GM-XileGM-Xile: check my answer :) it works perfectly. – Sudhakar Tillapudi Feb 22 '14 at 05:50
@GM-XileGM-Xile - see this discussion http://stackoverflow.com/questions/2859111/c-sharp-math-calculator – Ramesh Rajendran Feb 22 '14 at 05:52
Thank for you reply @RameshRajendran. I found the answer. – GM-Xile GM-Xile Feb 22 '14 at 05:56
@GM-XileGM-Xile - Update my code – Ramesh Rajendran Feb 22 '14 at 05:56

score 0 · Answer 3 · answered Feb 22 '14 at 05:50

You can compile code from string at runtime and execute it:

using Microsoft.CSharp;
using System;
using System.CodeDom.Compiler;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;

namespace DynamicCalcTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var result = new DynamicCalculator<double>("2 + 2 * 2").Execute();
        }
    }


    public class DynamicCalculator<T>
    {
        private MethodInfo _Method = null;

        public DynamicCalculator(string code)
        {
            _Method = GetMethodInfo(code);
        }

        public T Execute()
        {
            return (T)_Method.Invoke(null, null);
        }

        private MethodInfo GetMethodInfo(string code)
        {
            var tpl = @"
                public static class Calculator
                {{
                    public static double Calc()
                    {{
                        return {0};
                    }}
                }}";

            var finalCode = string.Format(tpl, code);

            var parameters = new CompilerParameters();
            parameters.ReferencedAssemblies.Add("mscorlib.dll");
            parameters.GenerateInMemory = true;
            parameters.CompilerOptions = "/platform:anycpu";

            var options = new Dictionary<string, string> { { "CompilerVersion", "v4.0" }     };

            var c = new CSharpCodeProvider(options);
            var results = c.CompileAssemblyFromSource(parameters, finalCode);

            var type = results.CompiledAssembly.GetExportedTypes()[0];
            var mi = type.GetMethod("Calc");
            return mi;
        }
    }
}

String calculator

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