Dynamically Creating and saving formula using C# code

Question

_{Thursday, August 20, 2009 10:12 AM}

I am working a C#.NET 3.5 application. I want to create complex formula using the values shown on the screen and save in XML or Database.

Eg:

Formula1 = (Value1 * Value2 + Value3)/Value6 - Value5

Formula2 = If (Value1 > 1000) then (Value1 * Value2 + Value3)/Value6 - Value5
else (Value3 * Value2 + Value1)/Value5 - Value6

For the given values, User should have an option to select the foruma from the list and do the calculation.

I also need an option to select the same formula and edit and then save.

How to create and save formulas using C# code?

How to give options to users to add operators like +,-,*,/ and braces while creating the formula?

Thanks
Ashok

All replies (6)

_{Thursday, August 20, 2009 2:47 PM ✅Answered | 2 votes}

You can also take a look at .NET 3.5 Expressions.

To generate an expression for

20.3 * Cos(30.2) + 20.1

You would say

 Expression ex = Expression.Add(
                Expression.Multiply(
                    Expression.Constant(20.3),
                    Expression.Call(null, typeof(Math).GetMethod("Cos"), Expression.Constant(30.2))
                    ),
                Expression.Constant(20.1)
                );

The variable Ex is now an expression tree as shown by Viral.

Unfortunetely, expression only support upto 4 variables. The example I have shown does not use any variables, but you can find examples for it.

If you want to run the expression to get the result, you need to make a lambda expression delegate, like so

            Expression<Func<double>> lEx = Expression.Lambda<Func<double>>(ex, new ParameterExpression[0]);

Now you can run the expression with the following

    lEx.Compile().Invoke();

When you create lEx, you can pass the variables in the call. If you want to create a variable, you can use something like

ParameterExpression x = Expression.Parameter(typeof(double), “x”);

which you can then use in the expression tree and in the creation of lEx.

The expression tree Ex can be traversed and then convered into a XML file or database table, you can then write a function to convert the XML back into the Expression tree in a similar fashion shown above.

Craig

Hope this helps abit.

Btw, .NET 4.0 has a whole host of new features for expression trees.

_{Thursday, August 20, 2009 10:54 AM | 1 vote}

You should think of a formula as tree Structure

For example (a * b) + (c / d)

can be thought of as

   +
       *
           a
           b
       /
           c
           d

Thanks,
Viral.

_{Thursday, August 20, 2009 2:01 PM | 1 vote}

Hi,
I hope it will help you.

private void Form1_Load(object sender, EventArgs e)
{
//Create 4 combo box with Formulla Conditions
FillCombo();
}
private void FillCombo()
{           
cmbValues.Items.Add("Values");
cmbValues.Items.Add("value1");
cmbValues.Items.Add("Value2");
cmbValues.Items.Add("Value3");
cmbValues.SelectedIndex = 0;

cmbOperators.Items.Add("opeartors");
cmbOperators.Items.Add("+");
cmbOperators.Items.Add("-");
cmbOperators.Items.Add("*");
cmbOperators.SelectedIndex =0;

cmbValues2.Items.Add("Values");
cmbValues2.Items.Add("value1");
cmbValues2.Items.Add("Value2");
cmbValues2.Items.Add("Value3");
cmbValues2.SelectedIndex = 0;

cmbConditions.Items.Add("Conditions");
cmbConditions.Items.Add("If");
cmbConditions.Items.Add("Else");
cmbConditions.Items.Add("OR");
cmbConditions.SelectedIndex =0;
}

private void btnFormula_Click(object sender, EventArgs e)
{
StringBuilder str = new StringBuilder();
String space = " ";
//Added ~ for single string Formulla
string seperator = "~";           
str.Append(cmbConditions.SelectedItem.ToString());
str.Append(seperator);          
str.Append(cmbValues.SelectedItem.ToString());
str.Append(seperator);
str.Append(space);
str.Append(cmbOperators.SelectedItem.ToString());
str.Append(seperator);
str.Append(space);
str.Append(cmbValues2.SelectedItem.ToString());
str.Append(space);           
MessageBox.Show(str.ToString());
SaveFormulla(str.ToString());

}

private void SaveFormulla(string formula)
{
//save ur formulla to DB or File..
StreamWriter wrter = new StreamWriter(@"c:\\text.txt");
wrter.WriteLine(formula);
wrter.Close();
}

private void LoadFormulla()
{
//Get the saved Formulla
StreamReader rdr = new StreamReader(@"c:\\text.txt");
string line = rdr.ReadLine();
rdr.Close();

if (!String.IsNullOrEmpty(line))
{
    String[] lua=line.Split('~');
    //Load Values To Combo box
}
}

private void button1_Click(object sender, EventArgs e)
{
//Load the Formulla again Combo
LoadFormulla();
}

Best Regards, C.Gnanadurai Please mark the post as answer if it is helpfull to you

_{Thursday, August 20, 2009 3:42 PM}

Hi Gnanadurai,

After saving the formula i also need to bind the values to variables in the formula and calculate the value.

If A*B + C is the formula, i need to set A=10 ,B =20 and C =50 and calculate the value using the formula.

how to bind values to the formula and calculate the result?

thanks
Ashok

_{Friday, August 21, 2009 1:33 PM}

Thanks Craig. Your post was helpful

Ashok

_{Wednesday, December 7, 2011 3:02 PM}

I don't know if this is too late, but I was looking for a similar requirement and found this wonderful library which does most of simple arithmetic. It does not however include complex math functions.. It solved my problem.

http://www.codeproject.com/KB/recipes/dynamicformula.aspx

Hope this helps..

Reagrds

Krishna J Vedula

Last updated on 2009-08-20

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Dynamically Creating and saving formula using C# code

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