关于 C# DataTable.Compute() 的语法

Question

While trying to find a simple C# math calculator, I have found one below. C# Math calculator

It is ideal for me since it does not need any COM or other third-party reference. However, I find out a confusing thing:

new DataTable().Compute("2-3/4*12", null) // Works fine, answer is -7;
new DataTable().Compute("2 / 0", null)    // Works but not correct, answer is 8;
new DataTable().Compute("100 / 0", null)  // Works but not correct, answer is 8;
new DataTable().Compute("2.0 / 0", null)  // Throw System.DivideByZeroException as estimated.

So I would like to ask, what's wrong with the second and third lines? Is the compute method treat the "/" is another way?

I have read this: https://msdn.microsoft.com/en-us/library/system.data.datatable.compute.aspx , but nothing helpful.

Answer 1

I Tried your code in LinqPad with the following results:

new DataTable().Compute("2 / 0", null); // Gives infinity (object{double})
new DataTable().Compute("100 / 0", null); // Gives infinity (object{double})
new DataTable().Compute("100 / 0", null); // Gives divideByZeroException

From my testcode:

        var result = (double) new DataTable().Compute("20 / 0", null);

        if(double.IsInfinity(result))
        {
            Console.WriteLine("Oh noes!"); // Debugger lands here
        }
        Console.WriteLine(result);
    }

The concept of infinity exists in double. I'm not sure why you get the exception on the last one though. Hopefully someone can comment on that.

Answer 2

Part of this question has already been answered: Why is infinity printed as "8" in the Windows 10 console?

We have an application that on Windows 8.1 will print "Infinity" for an expression such as "1 / 0". On Windows 10, it returns "8".

It's not a numeric value of 8, but an incorrectly displayed Unicode character (which should be a dead-8).