title: Android card guessing game throws MainActivity not declared among other errors
body: <p>I tried to build and run from the following <a href="http://www.programering.com/a/MzM4QTMwATI.html" rel="nofollow noreferrer">sample</a> but I'm getting couple errors: </p>
  
  <blockquote>
    <p>1- Error running MainActivity: The activity 'MainActivity' is not declared in AndroidManifest.xml<br>
    2- Error:(553, 69) String types not allowed (at 'activity_horizontal_margin' with value '').<br>
    3- Error:Execution failed for task ':app:processDebugResources'.>
    com.android.ide.common.process.ProcessException: Failed to execute aapt  </p>
  </blockquote>
  
  <p>Can somebody tell me what I'm missing?</p>