# Regular expression for US and Canada phone number


This a quick post regarding how to validate US and Canada phone number in very possible formats.

Requirements:

To determine whether a user entered a North American phone number in a common format, including the local area code. The supported formats are 1234567890, 123-456-7890, 123.456.7890,  123 456 7890, (123) 456 7890, and all related combinations. If the phone number is valid, we will convert that our standard format,  (123) 456-7890, so that the phone number records are consistently recorded.

Suggested expression: ^\\(?(\[0-9\]{3})\\)?\[-. \]?(\[0-9\]{3})\[-. \]?(\[0-9\]{4})$

Valid phone number series for the expression:

- 123-456-7890
- 123 456-7890
- 123-456 7890
- (123)-456-7890
- 123 456 7890

 

## .NET C# Code Snippet

```csharp
string userInput = txtPhoneNumber.Text;

Regex regexPhoneNumber = new Regex(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$");

if (regexPhoneNumber.IsMatch(userInput))
{
	string formattedPhoneNumber = regexPhoneNumber.Replace(userInput, "($1) $2-$3");
}
else
{
	// Invalid phone number
}
```

The following layout breaks the regular expression into its individual parts, excluding the repeating groups of digits:

| ^ | Assert position at the beginning of the string. |
| --- | --- |
| \\( | Match a literal "(" |
|   ? | between zero and one time. |
| ( | Capture the enclosed match to back reference 1 |
|   \[0-9\] | Match a digit |
| {3} | exactly three times. |
| ) | End capturing group 1. |
| \\) | Match a literal ")" |
| ? | between zero and one time. |
| \[-. \] | Match one character from the set "-. " |
| ? | between zero and one time. |
| ? | \[Match the remaining digits and separator.\] |
| $ | Assert position at the end of the string. |

Here, '**^**' and '**$**' are meta-characters named an _anchor_ or _assertion._ '^ is used to mask the start of regular expression and $ is used to mark the end. '$' is used to stop matching too much string into final result than required.

 

**For people seeking more information regarding the expression are suggested to visit detailed post here:** [http://blog.stevenlevithan.com/archives/validate-phone-number](http://blog.stevenlevithan.com/archives/validate-phone-number)

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