Recursion and Repetition 2 9 2011 Opening Discussion Minute essay comments Copy and paste commands in vi Let s look at solutions to the interclass problem Finishing the intersecting squares The match Expression There is a second conditional expression in Scala called match expr match case pattern expr case pattern expr There are lots of options for the pattern but the simplest one is literal values Lowercase names will be bound as val declarations Motivation We have the ability to do things once and to control whether or not certain things happen that once Computers are really great for doing things multiple times Reading a whole file or doing something until the user tells us to stop Mathematical Recursion The idea of recursion comes from mathematics A function is recursive if it is defined in terms of itself All recursive functions will have at least two cases One where the function refers to itself A base case where it doesn t refer to itself Let s look at some examples of this Programmatic Recursion Now I want us to write some Scala functions that are recursive They will look much like the math functions We have to provide a return type One argument changes to tell us when to stop Scripts and Redirection One way to process data from a file is to write a script and use redirection scala script scala input txt This way you don t have to enter the input over and over Also handy if the input is really large We ll learn other ways to deal with files later Minute Essay Make sure you are reading What questions do you have about this topic Minute Essay Make sure you are reading What questions do you have about this topic
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