think of local and global variable names much like you would a person's name. If you are talking around the water cooler and you say "barack is doing a good job", the other folks will likely assume you mean barack obama. If however, your CEO is named barack, they will probably assume the more local barack, and think of their boss. In that case, you would have to say barack obama to differentiate between the global barack (obama) and the local barack (your boss).
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