Question

I have to parse a string. It contains one or two numbers.

It can has 3 froms.

1. {number1}-{number2}
2. {number1}-
3. -{number2}

The numbers can be negative.

So for example:

• 100-200 means: number1 = 100, number2 = 200
• -100 means: number1 = null, number2 = 100
• 200- means: number1 = 200, number2 = null

now the harder part:

• -100-200 means: number1 = -100, number2 = 200
• -100- means: number1 = -100, number2 = null
• –100 means: number1 = null, number2 = -100
• 100–200 means: number1 = 100, number2 = -200

• -100–200 means: number1 = -100, number2 = -200

• -100-200- means: throw new FormatException(). its not a valid string.

Anything that cannot be parsed as 2 ints throws a formatexception (int.Parse does this, so it can be depended on).

I need a parser to parse it to two int? -s (nullable ints).

Every string is either valid (it makes sense), or invalid (it does not makes sense). There is no string that can mean 2 things (at least I didn’t find one).

If I het the 2 value, I want it to return in a tuple.

I get tangled up in the ifs.

Answer 1

(Editing to add the updated regex from the comments)

It seems like you could use the Regex class to figure this out, since your syntax is fairly regular and structures:

var regex = new Regex(@"^(?<first>-?[\d.,]+)?-(?<second>-?[\d.,]+)?$");
var match = regex.Match(input);
if (match.Success)
{
  int? a = match.Groups["first"].Success
    ? Int32.Parse(match.Groups["first"].Value) 
    : (int?)null;

  int? b = match.Groups["second"].Success
    ? Int32.Parse(match.Groups["second"].Value) 
    : (int?)null;
}