public override ValidationResult InsureeNumber(string insureeNumber) { if (insureeNumber.Length != 9) { return(new ValidationResult("Invalid CHF ID")); } String Chfid; int Part1, Part2; Part1 = int.Parse(insureeNumber.ToString()) / 10; Part2 = Part1 % 7; Chfid = insureeNumber.Substring(0, 8) + Part2.ToString(); if (insureeNumber.Equals(Chfid)) { return(ValidationResult.Success); } else { return(new ValidationResult("Invalid CHF ID")); } }