Getting Help

1. AbstractionIS 101Y/CMSC 101Computational Thinking and DesignTuesday, September 17, 2013Marie desJardinsUniversity of Maryland, Baltimore County

2. Getting Help • CSEE Help Center • ITE 201E – hours TBA but usually M-F 10-5, plus evening hours on some days • http://www.csee.umbc.edu/resources/computer-science-help-center/ • Tutors may not know Processing, but all know Java (which is similar) and are very helpful! • IS Java Lab (?)

3. Abstraction • Abstraction is the process of generalizing away from the details of a problem to simplify and focus on its key aspects • We use abstraction for problem solving, design, organization, and simplification • Examples from everyday life: • Smart thermostats • Steering wheels • Email folders and labels • Schedules and calendars • Language!!

4. Abstraction in Computing • Abstraction is ubiquitous in all computing disciplines • “It’s All Just Bits” • The interpretation (meaning) of data depends on how it is used • The same bit sequence can represent an integer, a decimal number, a sequence of characters, or anything else you might decide it means • Layers of computing hardware, including gates, chips, and components • Programming languages are abstractions of machine language • Functional decomposition == layers of abstraction • Models and simulations: abstractions of real-world phenomena • We can study, analyze, and experiment with models more easily than experimenting on the real world

5. Programming Enables Problem Solving, Expression, andKnowledge Creation • Programs are written to execute algorithms • Requires an understanding of how instructions are processed • Programs are executed to automate processes • A single program can be run multiple times, on many machines • Executable programs increase the scale of solvable problems • Programming is facilitated by appropriate abstractions • Functions are re-usable programming abstractions • Parameterization can be used to generalize a specific solution • Data abstraction can separate behavior from implementation • APIs and libraries simplify complex programming tasks • Programs are developed and used by people • Developing programs is an iterative process • Finding and eliminating errors is part of the process • Documentation isneeded for maintainable programs

6. Big Idea:Design • Problem solving often produces multiple possible solutions • Or multiple ways to implement the solution • Designis the process of making those decisions and choices • Design at a high level • Is it cost-effective to automate kidney exchange? • Should we use a relational or object-oriented database? • Design at a low level • How do I structure this function? • What do I call this variable?

7. Design Processfor Programs • First, understand the problem clearly • Second, write the solution in English • Testits correctness by manually applying it to some simple – and then more complex -- examples • Optionally, “translate” the solution into pseudocode • Advanced programmers will use this step as an abstraction to avoid the syntactic details of a particular programming language • Next, translate the solution into a programming language • Finally, implement (type) and test (carefully!) your solution

8. Example: Counting • Print the numbers from one to N • N is a variable that can change each time the program is called [an abstraction!!] • For example, “printNumbers (7)” should print:1 2 3 4 5 6 7

9. Counting in English:Attempt #1 • First attempt at English: Count from one to N Print out each number • Not really an algorithm – just a restatement (what is the primitive action “count”??)

10. Counting in English:Attempt #2 • Next attempt:Set the variable “current” to 1 Print the value of “current” Add one to “current” If “current” is greater than N, stop Otherwise, go back to “print” step • Turns out that “go to” statements are bad design (for reasons we’ll talk about later) • Let’s try it again, using something that looks more like a loop with a condition

11. Counting in English:Attempt #3 (almost right!) Set the variable “current” to 1 While “current” is less than N: Print the value of “current” Add one to “current” • Test by hand: what if N = 3? • Boundary cases: what if N = 0? N = -4? • Possible error cases: what if N = 8.73? what if N = “this isn’t a number”?

12. Counting in English:Processing Version void printNumber (int N) { int current = 1; while (current <= N) {println (current); current = current + 1; } }

13. Exercise #1: Multiplication • Work in your team – OK to split into smaller groups of 2 or 3 when you’re at the implementation step • How would you multiply two numbers, using only the addition operator? • Understand the problem – state some examples • Write the solution in English • Test the English solution! • Write the solution in Processing • Test the program! • Concepts: iterations, efficiency

14. Exercise #2: Guessing • With your team, write Processing code to guess a number between 1 and 100 • Remember the algorithmic design process: • Understand the problem – work through some examples by hand! • Write a solution in English and test it – then get a TF or instructor to OK your solution before moving on! • Translate your solution into Processing • Implement, test, and show a TF or instructor! • Be prepared to explain why your approach is a good way to solve the problem