C# Regex: Checking for “a-z” and “A-Z”

Question

I want to check if a string inputted in a character between az or AZ. Somehow my regular expression doesn't seem to pick it up. It always returns true. I am not sure why, I gather it has to do with how I am writing my regular expression. Any help would be appreciated.

private static bool isValid(String str)
{
    bool valid = false;

    Regex reg = new Regex((@"a-zA-Z+"));

    if (reg.Match(str).Success)
        valid = false;
    else 
        valid  = true;     

     return valid;
}

Answer 1

Regex reg = new Regex("^[a-zA-Z]+$");

• ^ start of the string
• [] character set
• \\+ one time or the more
• $ end of the string

^ and $ needed because you want validate all string, not part of the string

Answer 2

The right way would be like so:

private static bool isValid(String str)
{
    return Regex.IsMatch(str, @"^[a-zA-Z]+$");
}

This code has the following benefits:

• Using the static method instead of creating a new instance every time: The static method caches the regular expression
• Fixed the regex. It now matches any string that consists of one or more of the characters az or AZ. No other characters are allowed.
• Much shorter and readable.

Answer 3

使用

Regex.IsMatch(@"^[a-zA-Z]+$");