title: Android Dev - R.layout.main , Variable 'R' cannot be resolved
body: <p>We are new to Android and we are trying to develop a new application. We installed all the basic setup of Android. We tried to run the Android Sample projects in Eclipse. But while to compile the following lines and a few other lines that uses the variable 'R' throws up an error. </p>
  
  <p>setContentView(R.layout.activity_main);</p>
  
  <p>'R cannot be resolved to a variable'. I do not understand what is causing the error. Anyone help me out in this issue.</p>