any easier way to parse and solve expression in C#?

Question

I am trying to evaluate expressions that are inputted as strings

example: string svar1="1 * 2 * 3";

I need to be able to evaluate that to answer 6.

I am thinking about parsing it by spaces, then match the operators with switch to each functions (need to do +,-,*,/,%, etc) but it seems like a very tedious way as there are so many operators to code. Is there a way to convert a char/string containing an operator into actual operator?

If it is not a homewok you can use NCalc, otherwise, you will follow the path of all students.. — EZI, Feb 13 '15 at 20:17

score 4 · Answer 1 · answered Feb 13 '15 at 20:18

4

one easy way is to use DataTable.Compute Method

    static void Main(string[] args)
    {
        DataTable table = new DataTable();

        var result = table.Compute("1 * 2 * 3","");
    }

answered Feb 13 '15 at 20:18

Fredou

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An interesting, if not completely abusive and hacked, approach. This may not work for more *complex* expressions. – BradleyDotNET Feb 13 '15 at 20:19
@BradleyDotNET, I don't know the limit of it but you always need to test to make sure you get want you want :-) – Fredou Feb 13 '15 at 20:21
@BradleyDotNET: Abusive in the sense of using an elephant gun to kill a flea. Not hacked at all -- parsing and evaluating mathematical expressions is a core requirement of the `Compute` method. There's just additional ability for those expressions to include field accesses which won't be used here. – Ben Voigt Feb 13 '15 at 20:23
How does this satisfy the documented requirement that "the expression parameter requires an aggregate function" ? – Ben Voigt Feb 13 '15 at 20:25
@BenVoigt 1 and 2 and 3 are actually 3 aggregated values – Fredou Feb 13 '15 at 20:26

score 1 · Answer 2 · answered Feb 13 '15 at 20:17

1

No, this functionality is not included in any standard .NET assembly. Your method, in addition to being tedious, is going to be error prone.

You are looking for a math expression parser, NCalc is one such library.

answered Feb 13 '15 at 20:17

BradleyDotNET

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System.Data.DataTable does have it – Fredou Feb 13 '15 at 20:19
@Fredou In a very hacked/abusive way, yes. Given that it was intended for *database* expressions, using it in place of a math parser probably isn't the best idea. – BradleyDotNET Feb 13 '15 at 20:20

score 0 · Answer 3 · edited May 23 '17 at 12:27

0

Looks like a library called NCalc can accomplish what you need.

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

edited May 23 '17 at 12:27

Community

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answered Feb 13 '15 at 20:17

John M Fecko

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score 0 · Answer 4 · answered Feb 13 '15 at 20:20

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If you want some insight/code to demonstrate how this is done properly, using correct rules of precedence, in C# this is a good sequence of articles:

http://ericwhite.com/blog/map/recursive-descent-parser/

answered Feb 13 '15 at 20:20

James Gaunt

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any easier way to parse and solve expression in C#?

4 Answers4