double decimalValue = -1.5;
ulong integerValue; 

// Discard fractional portion of Double value
double decimalInteger = Math.Floor(decimalValue);

if (decimalInteger <= ulong.MaxValue && 
    decimalInteger >= ulong.MinValue)
{    
   integerValue = (ulong) decimalValue;
   Console.WriteLine("Converted {0} to {1}.", decimalValue, integerValue);
}   
else
{
   ulong rangeLimit;
   string relationship;
   
   if (decimalInteger > ulong.MaxValue)
   {
      rangeLimit = ulong.MaxValue;
      relationship = "greater";
   }   
   else
   {
      rangeLimit = ulong.MinValue;
      relationship = "less";
   }       

   Console.WriteLine("Conversion failure: {0} is {1} than {2}.",  
                     decimalInteger, 
                     relationship, 
                     rangeLimit);
}