C# evaluation string doesn't work

Question

I am trying to evaluate a math string and googled it a lot. I found a code snippet but didn't work for me. Here is the code

static decimal evaluate(string expression)
{
        var loDataTable = new DataTable();
         // ******* throws "The expression has a syntax error" message ******
        var loDataColumn = new DataColumn("Eval", typeof(double), expression);
        loDataTable.Columns.Add(loDataColumn);
        loDataTable.Rows.Add(0);
        return (decimal)(loDataTable.Rows[0]["Eval"]);
}

I am passing ((159,00)*(1,0)) as a string and throws

The expression has a syntax error

exception on the second line.

What do you think the problem is? thanks

Jonesopolis · Answer 1 · 2013-10-21T19:04:42.203

try this:

 public static void Main()
 {
    string expression = "((159,00)*(1,0))";
    decimal result = evaluate(expression.Replace(".","").Replace(",","."));
 }
 static decimal evaluate(string expression)
 {
    var loDataTable = new DataTable();
    var loDataColumn = new DataColumn("Eval", typeof(double), expression);
    loDataTable.Columns.Add(loDataColumn);
    loDataTable.Rows.Add(0);
    return decimal.Parse(loDataTable.Rows[0]["Eval"].ToString());
 }

as I understand European notation, commas and periods are switched. So first remove any periods, then replace commas with periods using this:

expression.Replace(".","").Replace(",",".")

(to ensure a string like ((159.162,00)*(2,0)) doesn't break)

Also, note the return is changed to decimal.Parse(), and it works well

dognose · Accepted Answer · 2013-10-21T19:07:10.550

3

You need to use . instead of , ( := ((159.00)*(1.0))

Oh, on a side node:

You need to invoke DataTable.compute() to invoke a evaluation of the expression:

 static decimal evaluate(string expression)
 {
    var loDataTable = new DataTable();
    return (decimal)(loDataTable.Compute(expression, ""));
 }

edited Oct 21 '13 at 19:07

answered Oct 21 '13 at 18:54

dognose

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I will try but decimal has commas.how can I convert commas to dots? – Arif YILMAZ Oct 21 '13 at 18:56

score 2 · Answer 3 · answered Oct 21 '13 at 19:03

First I thought maybe you need to set the culture so that it expects , not . as decimal separator.

But from here: http://msdn.microsoft.com/en-us/library/system.data.datacolumn.expression.aspx

All literal expressions must be expressed in the invariant culture locale. When DataSet parses and converts literal expressions, it always uses the invariant culture, not the current culture.

So, you must convert, but it may not be as simple as ,->., do you have and thousand separators in your culture? That needs to be changed also.

score 1 · Answer 4 · answered Oct 21 '13 at 18:57

1

You should use dot instead of comma:

expression.Replace(",",".")

answered Oct 21 '13 at 18:57

Yosi Dahari

6,794
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ceyun · Answer 5 · 2014-08-15T12:26:09.707

1

Maybe you can use/develop a parser like that

      string m_str = "((159,00)*(1,0))";
    List<string> m_newList = new List<string>();
    for (int i = 0; i < m_str.Length; i++)
    {
        if (m_str[i].ToString() == ",")
        {
            m_newList.Add(".");
        }
        else
        {
            m_newList.Add(m_str[i].ToString());
        }
    }

or use below code as you see many times in this page.

             expression.Replace(",",".")

edited Aug 15 '14 at 12:26

answered Aug 15 '14 at 11:52

ceyun

351
4
14

perhaps you could elaborate about the parser to be used / developed? The other part of your answer was indeed already an answer of someone else. – ljgw Aug 15 '14 at 11:58

score 1 · Answer 6 · answered Aug 15 '14 at 13:54

1

Actually, you can parse to a decimal dependant on culture. This way, you don't need all the replacing comma's and spaces. I believe you're turkish? then the below line will suit your needs.

decimal d = decimal.Parse(input, new CultureInfo("tr"));

answered Aug 15 '14 at 13:54

Jesse de Wit

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C# evaluation string doesn't work

6 Answers6