title: C# Regex: Checking for "a-z" and "A-Z"
body: <p>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. </p>
  
  <pre><code>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;
  }
  </code></pre>