Regular expression for single number or groups with addition (+) and subtraction (-) mathematical operator

Question

I need to create a regular expression that only accepts numbers and addition and subtraction characters.

I've defined the single number and groups pattern by this way ([1-9][0-9]*)

I'm not able to add the definition for addition and subtraction characters.

I'd like to have all ok with something similar this example

Ex: 12 + 1 - 23 - 9 + 10

Answer 1

To achieve validation, I would recommend you tokenize it, but organize it by looking for an operator [+-] first then the number. Once tokenized you can verify in code if all operations are valid and accumulate a resultant total.

Example

var data = "12 + 1 - 23 - 9 + 10";

var pattern = @"(?<Operator>[+-]*)\s*(?<Number>\d+)";

var tokens =
   Regex.Matches(data, pattern)
        .OfType<Match>()
        .Select (mt => new
             {
                 Operator = string.IsNullOrEmpty(mt.Groups["Operator"].Value)
                                  ? "+"   // Default to '+' if not found. (First Number)
                                  : mt.Groups["Operator"].Value,
                 Value    = mt.Groups["Number"].Value
             });

Result To Accumulate

Note it would also work if the numbers start out negative such as -12 + 1 - 23 - 9 + 10 result:

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Frankly one could be adding negative numbers. Here is a pattern to handle the sign of the number and process the sign and the operator together to determine and positive or negative accumulation:

var data = "-12 + 1 + -2 - -3";

var pattern = @"(?<Operator>[+-]*)\s*(?<Sign>[-]*)\s*(?<Number>\d+)";

var tokens =
   Regex.Matches(data, pattern)
        .OfType<Match>()
         .Select (mt => new
                  {
                    Operator = string.IsNullOrEmpty(mt.Groups["Operator"].Value)
                                     ? 1   // default to + if not found (First Number)
                                     : mt.Groups["Operator"].Value == "-" ? 0 : 1,
                    Sign     = string.IsNullOrEmpty(mt.Groups["Sign"].Value)
                                     ? 1   // default to positive
                                     : 0,
                    Value    = mt.Groups["Number"].Value
                  })
         .Select (token => new
              {
                  Postive = (((token.Operator & token.Sign) > 0) || 
                             ((token.Operator + token.Sign) == 0)) 
                             ? "+" : "-",
                  Value = token.Value
               })

Result To Accumulate

Note that minus a -3 makes it a +3 when accumulated. ;-)

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For completeness, here is a snapshot of the first Select before the operator and sign determination of the following second Select is done:

Which shows that two zeros signify two minuses, which need to be converted to a plus.