Regular Expression Quantifiers in *, +, ?, {, and } characters

This blog will demonstrates how to write the regular expression for matching occurrence like 0 or more, 1 or more or 0 or 1 or exact number matches or range matches

1.       Occurrence matches ( 0 or more, 1 or more or 0 or 1)

a*           -  0 or more

a+           -  1 or more

a?           -  0 or 1

 Example:  Input values contains alpha numeric but it may contains special character ‘%’ on first position but occurrence will be 1 or 0:

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string regExpression = @"^[%]?[a-zA-Z0-9]*$"; string input = "%Rajeev12"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  True

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string regExpression = @"^[%]?[a-zA-Z0-9]*$"; string input = "Rajeev123"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  True

In this scenario, input value have more than 1 special character ‘%'

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string regExpression = @"^[%]?[a-zA-Z0-9]*$"; string input = "%%Rajeev123"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

 Console Output:  False

 2.        Exact Matches:

a{5}  - exactly five length

a{2} - exactly two length

 Example:  Input values contains alpha numeric but length should be 4

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string regExpression = @"^[a-zA-Z0-9]{4}$"; string input = "123b"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  True

string regExpression = @"^[a-zA-Z0-9]{4}$";
string input = "1234b";        
Console.WriteLine(Regex.IsMatch(input, regExpression));
Console.ReadKey();

Console Output:  False

 3.       Matches between ranges

              a{1,3}    between one & three

Example:  Input values contains alpha numeric but length should be between 1 and 3

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string regExpression = @"^[a-zA-Z0-9]{1,3}$"; string input = "123b"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  False

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string regExpression = @"^[a-zA-Z0-9]{1,3}$"; string input = "123"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  True

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string regExpression = @"^[a-zA-Z0-9]{1,3}$"; string input = "23"; Console.WriteLine(Regex.IsMatch(input, regExpression)); Console.ReadKey();

Console Output:  True

Other related Posts:

C# Regex for alphabet, number and alpha-number

Regular Expression Quantifiers in *, +, ?, {, and } characters