Dynamic if statement evaluation/generation

Question

3.75/5 (4 votes)

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Hello everyone,

I want to evaluate dynamic if statement like the e.g below

int a=2;
String condition="a==2";

if(condition)
execute something
else
execute something

I mean that the condition is changeable, and it's coming from database.
For example:

String condition="";
int a, b, c, d;

....
The condition could be:

condition = "a == 2";

or could be:

condition = "a >= b && c == a && ((d - 4) == a ) ";

or

condition = ".....something else......";

if(condition)
execute something
else
execute something

The condition is not constant. That's my problem.

How i can do this... Please let me know..
Thanks in advance

[Modified: just changed the code tags to pre tags...a bit easier to read that way IMO]

Posted 18-Oct-10 2:48am

worker.db

Updated 20-Oct-10 7:09am

William Winner

v5

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4 solutions

Solution 4

It might be possible using the .NET framework built in code compiler. I have never done this myself, but i have seen demos of it done with IronRuby, etc. Admittedly they were dynamic languages, but should be possible to do it in C#.

This[^] article on CodeProject might help.

There is also a calculator example here[^].

If the user is able to enter the a ==2 etc, you will have to be very careful checking input to make sure they don't do anything nasty. Not sure how you would go about doing this.

Posted 18-Oct-10 11:44am

aj.esler

Solution 1

I am not very clear about your question.

What's the problem with the below code (C#):

C#

int a = 2;
if (a == 2)
{
    //execute something
}
else
{
    //execute something else
}

And what do you mean by evaluating dynamic if statement?

Posted 18-Oct-10 2:59am

Ankur^\m/

Solution 6

hi ,
your code snap is like this :

int a=2;
String condition="a==2";

if(condition)
execute something
else
execute something
Right?
You have to declare your "condition" variable in "dynamic" keyword instead of "string".

Posted 28-Mar-12 3:34am

gaurav modi

Comments

Andreas Gieriet 28-Mar-12 16:25pm

dynamic does not help here. Your understanding of dynamic is wrong.
See C# dynamic keyword. The object declared dynamic tells the runtime environment to search for the member at runtime before executing it. What we have here is a string and we do not call anything on it. Instead, it has to be parsed before executed.
- use the code DOM provider
- use Dynamic LINQ or one of the many hand-crafted variants thereof, e.g. my alterantive tip
- any google: C# expression evaluator that lingers around in the web...
Cheers
Andi

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Nish Nishant · Accepted Answer · 2010-10-18T03:50:00

Solution 3

You need to write an expression evaluator that can take a string, parse it, and evaluate a mathematical expression with variables. There's nothing built-in that can do this, so you need to write your own or search for a 3rd party implementation.

Posted 18-Oct-10 3:50am

Nish Nishant

Comments

Ankur^\m/ 19-Oct-10 3:40am

Okay, I missed the question completely. :(