How to convert string to bool and evaluate the condition?

Question

I have to convert a string to bool and evaluate the string condition. For example:

string condition = "8 > 9 || !8";

then the condition has to evaluate and return true;

if string condition = "!8"; then condition has to return true.

Suggest me how to evaluate the condition.

It depends on how reliable the structure of the string is. How many different operators do you expect to have to process?. What code have you written so far? — ste-fu, Feb 17 '20 at 11:31
it seems like what you're really after here is an runtime expression parser and evaluator; that *isn't really a thing built into .NET* directly, but a range of tools exist. Or depending on the complexity of the expressions you need to parse, it is *usually* relatively easy to write them yourself, if you're used to things like AST evaluation. — Marc Gravell, Feb 17 '20 at 11:32
btw; it isn't clear to me what `!8` means, as a boolean; is that meant in a C-style "zero is false, non-zero is true" way? — Marc Gravell, Feb 17 '20 at 11:33
That's essentially some kind of parser, which will read your equations, determine operators and left/right side operands, have some kind of validation. There is no short answer to that. — SᴇM, Feb 17 '20 at 11:33
@ste-fu , || , &&, !, <, <=, >, >= are the operators i have. Upto to now i just resolved the string values in place of 8 and 9. — Kalyani Reddy, Feb 17 '20 at 11:33
I have a condition with registry keys like "REGISTRYVERSION > CURRENTVERSION OR NOT REGISTRYVERSION". I resolved the registry key values like the above condition resolved to 01.00.00.000 > 02.00.00.000 || !01.00.00.000.. Can some one suggest me how to resolve this condition and return bool value — Kalyani Reddy, Feb 17 '20 at 11:36

score 2 · Accepted Answer · answered Feb 17 '20 at 12:48

Generally, if you want to evaluate C# code during runtime, you can use the .NET Compiler Platform (Roslyn) via the Microsoft.CodeAnalysis.CSharp.Scripting Nuget package.

BTW, I found this right here in stack overflow: How can I evaluate a C# expression dynamically?

here's a solution to your specific requirement, assuming the only exception to valid C# expressions is treating !8 as boolean true (specifically "!8" preceded or followed followed by any other character is forbidden).

private async Task<bool> ProcessExpression(string expression)
    {
        var processedExpression = expression.Replace("!8", "true");
        return await CSharpScript.EvaluateAsync<bool>(processedExpression);
    }

And here's some test code for the above:

Task.Run(async () =>
        {
            var expresion = "8 > 9";
            var result = await ProcessExpression(expresion);
            Console.WriteLine($"{expresion} : {result}");

            expresion = "8 < 9";
            result = await ProcessExpression(expresion);
            Console.WriteLine($"{expresion} : {result}");

            expresion = "!8";
            result = await ProcessExpression(expresion);
            Console.WriteLine($"{expresion} : {result}");

            expresion = "8 > 9 || !8";
            result = await ProcessExpression(expresion);
            Console.WriteLine($"{expresion} : {result}");

            expresion = "8 > 9 && !8";
            result = await ProcessExpression(expresion);
            Console.WriteLine($"{expresion} : {result}");
        });

The output we get is:

8 > 9 : False 8 < 9 : True !8 : True 8 > 9 || !8 : True 8 > 9 && !8 : False

please note that this solution has a performance penalty and if this is a concert than you should look for other options such as writing a dedicated parser or look for 3rd party Nuget packages.

score 0 · Answer 2 · answered Feb 17 '20 at 11:56

0

Try using the IValueConverter interface provided by .net

https://learn.microsoft.com/en-us/dotnet/api/system.windows.data.ivalueconverter?view=netframework-4.8

Where u define 2 methods Convert and ConvertBack Each method takes a parameter of type object and return the type object

so u can input the string and return the Boolean. As for the conversion from a string to expression you can checkout this link https://expressiontree-tutorial.net/knowledge-base/5029699/csharp-convert-string-expression-to-a-boolean-expression which have the required code cleared out.

answered Feb 17 '20 at 11:56

it really isn't obvious to me how `IValueConverter` would help here; that just defines an API - but, that isn't the problem here; the problem is implementing it! we could just as well forget about `IValueConverter` and say `bool DoTheThing(string expression) { /* TODO */ }` and we'd be in *exactly* the same position. The second link shown *is* relevant, though. – Marc Gravell Feb 17 '20 at 12:25
I didn't know exactly ur use case so i suggested the IValueConverter so u can use it in several situations like in xaml binding or any other usecase – Feb 17 '20 at 12:39
this is an old link but it is discussing the same issue https://stackoverflow.com/questions/5029699/c-sharp-convert-string-expression-to-a-boolean-expression – Feb 17 '20 at 12:39

How to convert string to bool and evaluate the condition?

2 Answers2

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