DataTable.Compute() raising an exception in C# WinUI

Question

I am creating a simple calculator app in WinUI with C#. I am using the Compute method in DataTable to solve the arithmetic problem. AnswerBox is a label where numbers and operators are appended, and an answer is displayed (using the compute function) when a button is clicked.

AnswerBox.Text = (string)new DataTable().Compute(AnswerBox.Text, "");

It raises an exception when I enter 2+2 (or any other valid expression) in the label. The exception is not shown in vs2022, the app crashes and opens the App.g.i.cs file showing the following.

#if DEBUG && !DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION
            UnhandledException += (sender, e) =>
            {
                if (global::System.Diagnostics.Debugger.IsAttached) global::System.Diagnostics.Debugger.Break();
            };
#endif

Look at e argument, it will contain the exception causing the crash. — Simon Mourier
– Simon Mourier, Commented Jun 16, 2024 at 16:51
It often helps to actually add the exception you get. They aren't equal you know. Here the result oft "2+2" is an integer and not a string. The exception should tell you that. — Ralf
– Ralf, Commented Jun 16, 2024 at 18:43
Apart from anything else, I would expect the exception to be displayed in the Output window, although perhaps it wouldn't happen until you continued from that point. — jmcilhinney
– jmcilhinney, Commented Jun 17, 2024 at 1:38
@jmcilhinney, I was expecting that too, but when I continue, it says the current debugger is unable to handle the exception. Now what does that mean? — Ninad Kulkarni
– Ninad Kulkarni, Commented Jun 17, 2024 at 2:53

Andrew KeepCoding · Accepted Answer · 2024-06-17 02:49:26Z

1

In this case, the following code returns an int value, 4 to be specific.

new DataTable().Compute(AnswerBox.Text, "");

The issue is that you can't just cast int to string.

The next code should work:

var dataTable = new DataTable();

if (dataTable.Compute(AnswerBox.Text, "") is int coputeResult)
{
    AnswerBox.Text = coputeResult.ToString();
}

answered Jun 17, 2024 at 2:49

Andrew KeepCoding

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1 Comment

Ninad Kulkarni Over a year ago

Thanks, @Andrew KeepCoding, I thought that compute converts the int result into string so I used string cast. I would also add an else if statement for decimal (float) as my calculator also has decimal operations :)

Ninad Kulkarni · Accepted Answer · 2024-06-17 03:14:35Z

-1

I later came up with a better solution -

var result = new DataTable().Compute(AnswerBox.Text, "");
AnswerBox.Text = result.ToString();

Now it can handle both int and decimal (practically anything xD).

answered Jun 17, 2024 at 3:14

Ninad Kulkarni

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