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

Question

I want to check if a string inputted in a character between a-z or A-Z. 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