Question

the field data has 4 acceptable types of values:

 j
 47d (where the first one-two characters are between 0 and 80 and third character is d)
 9u (where the first one-two characters are between 0 and 80 and third character is u)
 3v (where the first character is between 1 and 4 and second character is v).

Otherwise the data should be deemed invalid.

string data = readconsole();

what is the best way of validating this input?

I was considering a combination of .Length and Switch substring checks.

ie.

if (data == "j")

else if (data.substring(1) == "v" && data.substring(0,1) >=1 && data.substring(0,1) <=4)
....
else
   writeline("fail");

Answer 1

You can use a regular expression that matches the different kinds of values:

^(j|(\d|[1-7]\d|80)[du]|[1-4]v)$

Example:

if (Regex.IsMatch(data, @"^(j|(\d|[1-7]\d|80)[du]|[1-4]v)$")) ...

Explanation of the regular expression:

^ matches the beginning of string
j matches the literal value "j"
| is the "or" operator
\d matches one digit
[1-7]\d matches "10" - "79"
80 matches "80"
[du] matches either "d" or "u"
[1-4] matches "1" - "4"
v matches "v"
$ matches the end of the string