regex in c#

@Basit Nisar

You can use the below code

 

numericregex = @"^[0-9]{4,18}"

The provided regular expression ^[0-9]{5} is designed to match a string that:

• ^ asserts the start of the string.
• [0-9] matches any digit from 0 to 9.
• {5} specifies that there should be exactly five digits.

So, ^[0-9]{5} matches a string that starts with exactly five digits.

If you want to modify this regex to set a minimum of 4 and a maximum of 18 digits, you can use the following pattern:

string numericRegex = @"^[0-9]{4,18}";
 

string regexPattern= @"^\d{4,18}$";

 

it will allow min 4 digit and max 18 digits

Hi Nasir,

Please check below one,

using System;
using System.Text.RegularExpressions;

string input = "123"; // Example less then 4
string regexPattern = @"^\d{4,18}$";

bool isMatch = Regex.IsMatch(input, regexPattern);
Console.WriteLine(isMatch); // Output is false

using System;
using System.Text.RegularExpressions;

string input = "123234234"; // Example between 4 to 18
string regexPattern = @"^\d{4,18}$";

bool isMatch = Regex.IsMatch(input, regexPattern);
Console.WriteLine(isMatch); // Output is true

To modify the regular expression to match a minimum of 4 and a maximum of 18 digits, you can update it as follows:

numericregex = @"^[0-9]{4,18}"

The modification involves using a quantifier {4,18} after the character class [0-9]. This quantifier specifies that the preceding character class (digit) should occur at least 4 times and at most 18 times.

The expression @"^[0-9]{5}" is a regular expression pattern that matches a string consisting of exactly five numeric digits (0-9) at the beginning of the string. To enforce the minimum number of 4 and maximum number of 18 in C#, you can utilize the following pattern:

string numericRegex = @"^(?:[4-9]|1[0-8])$";