R cannot be resolved to a variable.

R cannot be resolved to a variable

R cannot be resolved to a variable or R.java file missing????

This is the most common error which occurs.
There are simple testing to overcome this error.

1.Check all the xml files in <my project>/res folder.
2.xml files means it may be layout files,string.xml, dimens.xml, styles.xml.

This error is occured because the ADT cannot build the code if there's any error in xml file, by which the project will not generate the automated generated java file means R.java file.