C# Preselected parameter values when calling a method

Question

I am trying to make a method/function, which can work in two modes: bits or hex.
the user(programmer) should call this method while passing value and mode parameter.
I'd like to limit the mode parameter to a string of "bin" or "hex". is it possible to generate a compiler error or warning (or pre-compiler error) when the user pass another unwanted value: such as "dec" ?

Example for acceptable parameters:

int decValueFromHex = convertToDec("111011","hex");
int decValueFromBin = convertToDec("111011","bin");

the below is not wanted, and need to generate an error somehow. (before final compilation)

int decValueFromDec = convertToDec("111011","dec");
int decValueFromMood = convertToDec("111011","hey");

Answer 1

No. You cannot apply rules on parameters like this. That's the entire point behind using an enum for example.

Try this:

enum Mode
{
    bin, hex
}

convertToDec("111011",Mode.hex);