How to return a double or string for a method

Question

I have a method:

public static double c(string val)
{
    return Math.Round(Convert.ToDouble(val), 4);
}

Where I pass in a string, and if its a double, I want to round then return a double, but if its a string, I want to return a string as is. All of the parameters that I pass in will be strings to start, how do i determine if its a string or double, and how do i rewrite the methoed to have the return type flexible enough to return either?

Ideally, I would like to use type variant like in vba, but i dont think there is an analog in c#.

Answer 1

The following will try to parse the double. If returns true it will put the double in the output variable output; else return false means val isn't a double and you should use the string val instead.

public static bool c(string val, out double output)
{
    if (double.TryParse(val, out output))
    {
        output = Math.Round(output, 4);
        return true;
    }
    else
    {
        output = 0;
        return false;
    }
}

Use like this:

string val = "123.45678";
double output;
if ( c(val, out output) )
{
    // use double output
}
else
{
    // val isn't a double, just use val directly
}

Answer 2

You can use typeof() and set your parameter of the function to object. Then you can pass everything to the function and can check the type with typeof().