Testing number inputs with special symbols

Digits in Regular Expression

Developers in most cases use regular expressions to verify number inputs.

There are two ways to match a digit via regular expression:

- [0-9] matches an Arabic numeral, i.e. 0,1,2,3,4,5,6,7,8,9;

- \d matches a Unicode number.

In addition to Arabic numerals Unicode contains more than 300 numbers from different cultures:

0: 0,٠,۰,߀,०,০,੦,૦,୦,௦,౦,೦,൦,๐,໐,༠,၀,႐,០,᠐,᥆,᧐,᭐,᮰,᱀,᱐,꘠,꣐,꤀,꩐,０
1: 1,١,۱,߁,१,১,੧,૧,୧,௧,౧,೧,൧,๑,໑,༡,၁,႑,១,᠑,᥇,᧑,᭑,᮱,᱁,᱑,꘡,꣑,꤁,꩑,１
2: 2,٢,۲,߂,२,২,੨,૨,୨,௨,౨,೨,൨,๒,໒,༢,၂,႒,២,᠒,᥈,᧒,᭒,᮲,᱂,᱒,꘢,꣒,꤂,꩒,２
3: 3,٣,۳,߃,३,৩,੩,૩,୩,௩,౩,೩,൩,๓,໓,༣,၃,႓,៣,᠓,᥉,᧓,᭓,᮳,᱃,᱓,꘣,꣓,꤃,꩓,３
4: 4,٤,۴,߄,४,৪,੪,૪,୪,௪,౪,೪,൪,๔,໔,༤,၄,႔,៤,᠔,᥊,᧔,᭔,᮴,᱄,᱔,꘤,꣔,꤄,꩔,４
5: 5,٥,۵,߅,५,৫,੫,૫,୫,௫,౫,೫,൫,๕,໕,༥,၅,႕,៥,᠕,᥋,᧕,᭕,᮵,᱅,᱕,꘥,꣕,꤅,꩕,５
6: 6,٦,۶,߆,६,৬,੬,૬,୬,௬,౬,೬,൬,๖,໖,༦,၆,႖,៦,᠖,᥌,᧖,᭖,᮶,᱆,᱖,꘦,꣖,꤆,꩖,６
7: 7,٧,۷,߇,७,৭,੭,૭,୭,௭,౭,೭,൭,๗,໗,༧,၇,႗,៧,᠗,᥍,᧗,᭗,᮷,᱇,᱗,꘧,꣗,꤇,꩗,７
8: 8,٨,۸,߈,८,৮,੮,૮,୮,௮,౮,೮,൮,๘,໘,༨,၈,႘,៨,᠘,᥎,᧘,᭘,᮸,᱈,᱘,꘨,꣘,꤈,꩘,８
9: 9,٩,۹,߉,९,৯,੯,૯,୯,௯,౯,೯,൯,๙,໙,༩,၉,႙,៩,᠙,᥏,᧙,᭙,᮹,᱉,᱙,꘩,꣙,꤉,꩙,９  

Using these Unicode numbers it is possible to test number inputs on correctness.
For example, in most cases it is expected that a phone number will contain only Arabic numbers. It is easy to check by providing special symbols, for example, "١٢٣" instead of "123", or some Indian Unicode numbers: ० (0), १ (1), २ (2), etc.

Below is an example of a valid Microsoft check for an Azure account recovery phone:

Code to generate special digit symbols

.NET considers[0-9] and \d as different expressions, below is the C# script to find all Unicode numbers:

 var stringBuilder = new StringBuilder();
 
 var digitRegex = new Regex(@"\d");
 var charDigitGroups = Enumerable.Range(Char.MinValue, Char.MaxValue)
                                 .Select(Convert.ToChar)
                                 .Where(ch => digitRegex.IsMatch(ch.ToString()))
                                 .GroupBy(ch => Char.GetNumericValue(ch));
 
foreach (var charGroup in charDigitGroups)
{
      string joinedValues = String.Join(",", charGroup);
      string rowResult = String.Concat(charGroup.Key.ToString(), ": ", joinedValues);
      stringBuilder.AppendLine(rowResult); 
} 

Some languages like JavaScript do not support Unicode in regular expressions by default, so there \d is the same as [0-9]. Nevertheless it is useful to check applications on the Unicode digital input independent on the realization details.

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