title: Method adds not a necessary line to a list when it should not do so
body: <p>I'm a beginner in c# and I am working with text exercises. I made a method to filter vehicle's plate numbers. It should consist of 3 letters and 3 integers ( AAA:152 ). My method sends the wrong plate numbers to a file, but also it adds that bad number to a good ones list. </p>
  
  <pre><code>private static string[] InvalidPlates(string[] csvLines, int fieldToCorrect)
  {
      var toReturn = new List&lt;string&gt;();
      var toSend = new List&lt;string&gt;();
  
      int wrongCount = 0;
  
      for (int i = 0; i &lt; csvLines.Length; i++)
      {
          string[] stringFields = csvLines[i].Split(csvSeparator[0]);
          string[] values = stringFields[fieldToCorrect].Split(':');
  
          if(Regex.IsMatch(values[0], @"^[a-zA-Z]+$") &amp;&amp; Regex.IsMatch(values[1], "^[0-9]+$"))
          {
              toReturn.Add(string.Join(csvSeparator, stringFields));
          }
          else
          {
              toSend.Add(string.Join(csvSeparator, stringFields));
              wrongCount++;
          }
      }
  
      WriteLinesToFile(OutputFile, toSend.ToArray(), wrongCount);
      return toReturn.ToArray();
  }
  </code></pre>
  
  <p>Can somebody help me to fix that?</p>