Basic Loops 9 21 2006 1 Opening Discussion What did we talk about last class Do you have any questions about the assignment Do you have any questions about the reading 2 Repetition Last time we decided that we wrote a little calculator and we ran into a problem when we wanted the calculator to do more than one calculation We got around this by having a function call itself This is called recursion and we ll spend more time on it in the future Recursion is not the normal way of getting plain repetition in C The more standard method is to use loops 3 Loops in General There are three general types of loops that occur in programming languages Loops also have something of a general structure that includes four elements Pre test loops Post test loops Counting loops Initialize Condition Loop body Iterate The order and nature of these elements can vary Forgetting one typically means that you have made a mistake 4 Loops in C What are the different loops that you have in the C language What type is each one When would you want to use each one 5 Adding Loops to Code Let s change our calculator so it uses a loop for repetition instead of recursion We could even write code that can parse prefix math expressions If we add a bit of logic to our ray tracing code we could make it do something interesting like drawing our sphere 6 Repetition through Recursion As we saw last class we can do repetition by having a function call itself This is called recursion Recursion is an incredibly powerful tool In C you don t normally use recursion when a loop would suffice but there are many problems where recursion can easily do things that can t be done with loops without throwing in a lot of extra complexities The critical key for any recursion is that there has to be a chance for the function to not call itself 7 Minute Essay Write a function that will sum and return the numbers read from standard input until a value of zero is read Remember to turn in assignment 2 by midnight tonight Quiz 3 will be at the beginning of next class 8
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