I'm trying to convert a string to a double. If it encounters null value the value should then be 0 (zero). However, it comes up with an error message:
"Operator '??' cannot be applied to operands of type 'double' and 'double'. It's sort of confusing because both numbers are double? How do I fix this?
double final = double.Parse(min.ToString()) ?? 0.0;
Maybe this, assuming min is a string:
double final = double.Parse(min ?? "0");
Or perhaps:
double final = (min == null) ? 0 : double.Parse(min);
EDIT
Even better:
double final = Convert.ToDouble(min);
Per the documentation, that method will return
A double-precision floating-point number that is equivalent to the number in value, or 0 (zero) if value is null.
This error appears because the left side of ?? must be a Nullable type that can take null as a value.
in your code:
double final = double.Parse(min.ToString()) ?? 0.0;
You are using ?? operator which called Null-coalescing operator and what this operator do is checking if double.Parse(min.ToString()) __evaluates to a value has the type of double (which is a value type)_ is null or not. if it wasn't null, then assign the value to final, otherwise assigned 0.0 to it.
Since double is a value type and a value type variables cannot be null unless they are Nullable, you will get an error, and that's why you are getting this error:
"Operator '??' cannot be applied to operands of type 'double' and 'double'."
To solve this, you can try this:
double final = Convert.ToDouble(min);
which return zero if min was null.
PS: try to avoid using the Parse method, which throw System.FormatExceptoin when it fails to parse, use TryParse instead:
string min = "2.s"; // not a number
double finals;
bool successed = double.TryParse(min, out finals); // true if successed, otherwise false.
Console.WriteLine(successed? $"Yes! finals = {finals}": $"No :( finals = {finals}");
// finals is 0 if the parse didn't work.
min? Can you share a complete example???has to be a nullable type.doublecan never be null, so it doesn't make sense to use??with it.