Why does VS think this statement is always true?

Question

Hi

I have this if statement -

if (!((main.property == 1)||(main.property == 2)))
{
   ...
}

main.property is a byte which is either 0, 1, 2 or 98.

Visual studios says that this statement is always true but I can't see why?

If the property is 1 or 2 shouldn't this be false.

Thank you in advance.

Edit: Added code

file1.cs

private void Upload(DataSet ds)
{
    Main main = CreateMain(ds); //This is tested and works correctly
    if(ValidateDate(main))
    {
        ...
    }
}

file2.cs

internal static bool ValidateData(Main main, ...)
{
    if (!((main.property == 1)||(main.property == 2)))
    {
        ...
    }
}

Edit: Added code

If I do this the error goes away -

internal static bool ValidateData(Main main, ...)
{
     main.property = 0; //Or = any number
     if (!((main.property == 1)||(main.property == 2)))
     {
          ...
     }
}

I'm guessing VS thinks it isn't initialised but I am 100% positive it is.

Answer 1

I wrote this little program to check it out:

    class Program
{
    static void Main(string[] args)
    {
        test(0);
        test(1);
        test(2);
        test(3);
        Console.ReadLine();
    }

    private static void test(int p)
    {
        bool b1 = (!((p == 1) || (p == 2)));
        bool b2 = (p != 1 && p != 2);
        Console.Out.WriteLine("{0} {1} {2}", b1, b2, b1 == b2);
    }
}

It seems that Constantin is right in his transcription, but neither expression is always true or always false.

Answer 2

Step through your code to find out what main.property value is.

I had a similar issue and it was because the value was null the default value.

Answer 3

Since you claim that main.property is a byte which is either 0, 1, 2 or 98, you should assert that condition at the beginning of that method as such:

internal static bool ValidateData(Main main, ...)
{
    System.Diagnostics.Debug.Assert(main.property == 0 || main.property == 1 || main.property ==2 || main.property == 98);
    if (!((main.property == 1)||(main.property == 2)))
    {
        ...
    }
}