Parse 2 numbers in C# divided by minus sign

Question

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

It can has 3 froms.

{number1}-{number2}
{number1}-
-{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.

Sounds like you've defined a bunch of the tests. Now have you _written_ these tests? — Austin Salonen, Mar 02 '12 at 17:56
Not sure if I understand the question correctly, but no. Only this structure is defined. I have not written tests. — vinczemarton, Mar 02 '12 at 17:58
can you show the actual code if you want nullable integer for example you can do the following int? myInt; — MethodMan, Mar 02 '12 at 18:01
@SoonDead: You have 9 tests defined in this question. Are you not familiar with TDD? — Austin Salonen, Mar 02 '12 at 18:03
Is this Homework? If it is add the Homework tag so that you get the right kind of help — Bronumski, Mar 02 '12 at 18:04
Is your fourth "harder" example correct? It looks like "100--200" should parse to 100, -200. — HABO, Mar 02 '12 at 18:18
@SoonDead - This is real work, seriously, how about providing us what you have attempted. — Security Hound, Mar 02 '12 at 19:53
@Ramhound : since I have only written about 4 ifs, and was not sure about the rest of them, I thought providing a definition of the problem is nearly as useful. — vinczemarton, Mar 02 '12 at 21:44
@AustinSalonen If you are referring to my examples of expected input-outputs in the question, then yes these were written by me, just to clarify the question. I have also tested the accepted answer against these. — vinczemarton, Mar 02 '12 at 21:46

score 8 · Accepted Answer · edited Mar 23 '12 at 08:01

8

(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;
}

edited Mar 23 '12 at 08:01

TDaver

7,164
5
47
94

answered Mar 02 '12 at 18:01

Michael Edenfield

28,070
4
86
117

This is great! I'll also need to parse decimals, which are culture invariant (so I can expect 5.02 but also 10,5). Can you help escaping these 2 characters too? – vinczemarton Mar 02 '12 at 18:10
3

@SoonDead: Regex(@"^(?-?[\d\.\,]+)?-(?-?[\d\.\,]+)?$") – mrbm Mar 02 '12 at 18:14
I have learned a great deal about using regex in C# from this. Like named groups. Thanks a lot. – vinczemarton Mar 02 '12 at 18:37
1

@mrbm: small nitpick: I don't think you need to escape `.` and `,` if inside `[]`. Not a mistake though... – TDaver Mar 22 '12 at 14:59

score 6 · Answer 2 · answered Mar 02 '12 at 17:58

6

Have you considered using a regular expression?

^(-?\d+)?-(-?\d+)?$

answered Mar 02 '12 at 17:58

dtb

213,145
36
401
431

Can you explain this a little more? If you can solve this with regular expressions and return the two int?-s, then it is great. – vinczemarton Mar 02 '12 at 18:02
@SoonDead: Have a look at the answer by Michael Edenfield. It's the same regular expression, but he also shows how to use it in C#. – dtb Mar 02 '12 at 18:03
@SoonDead you aren't going to get two int?s out of a regex -- it parses strings -- but once you get the string split into pieces it should be pretty easy from there. – Michael Edenfield Mar 02 '12 at 18:05

score -2 · Answer 3 · answered Mar 02 '12 at 18:08

-2

you could try .Split() method:

string testString = "100-200" ;

string[] results = testString.Split('-');

 int nr1;
 int nr2;
try
{
  nr1  = Convert.toInt32(results[0]);
  nr2  = Convert.toInt32(results[1]);
}
catch{}

answered Mar 02 '12 at 18:08

Alex Peta

1,407
1
15
26

Parse 2 numbers in C# divided by minus sign

3 Answers3