Determine about the Post conditions assertion

A  post condition is an assertion which should be true at completion of an operation. For instance, a post condition of the square root operation is that its result, when squared, is within a small amount of its argument. Post conditions generally specify relationships between arguments and results, or restrictions on results. Sometimes they specify that arguments don't change, or that they change in certain ways. Ultimately, a post condition may specify what happens when a precondition is violated (for instance, that an exception will be thrown).