Chapter 1 The Way of the Program

1. Chapter 1The Way of the Program Dr. Paige H. Meeker

2. Definition What is computer science all about?

3. A computer scientist is… A little bit of: • Mathematician • Engineer • Natural Scientist • Teacher • Educator But most of all – A PROBLEM SOLVER

4. Problem Solving / Programming • Computer scientist give computers lists of instructions (aka “programs”) in order to solve problems. • This semester, we will use the Python programming language to give instructions to our own programmable robot. • But first…

5. Programming Languages • Low level • High level

6. High Level Languages Advantages: • Easier to program • Faster to create • Shorter and easier to read • More likely to be correct • Portable

7. The Translation Process • Compiler • Interpreter • Some use both – Python uses both, but because of the way users interact with it, is considered more of an interpreted language

8. Python Interpreter • How do you use it? • Shell mode • Script mode

9. Shell Mode • Python commands typed into the shell are immediately interpreted and executed. • Instructions are typed at the Python prompt, which looks like: >>> • Once the shell session is terminated, all instructions given during that session are lost.

10. Script Mode • A program in a file • Name ends with “ .py” (perhaps we call it “firstprogram.py” • The file (or script) can then be run inside the interpreter’s shell with the command: >>>python firstprogram.py • Once the interpreter’s shell session is terminated, all instructions given during that session are lost, but all instructions held within a file are saved for use at a later time.

11. So… Now What? • We can give the computer (and/or the robot) a set of instructions which tell it what we wish it to do. This is called “Programming”

12. Computer Programming • What is computer programming? • Process of writing, testing, debugging, and maintaining the source code of computer programs.

13. Computer Programming • Why do we do it? • To create a program that performs a desired behavior. • There is some debate as to whether programming is an art, a craft, or an engineering discipline.

14. Computer Programming • Programmers work to create code that is efficient (works without draining current resources) and evolvable (can become something bigger in the future) • Programmers are generally given a list of requirements and then work to translate those requirements into something the computer can understand.

15. Computer Programming • Programming is often compared to following a recipe. • Programming is about giving the computer step by step instructions to go about completing the task. • The instructions generally take the form of: • a direct statement • a conditional statement • a link to a group of statements • a loop around statements meant to be repeated for some amount of time.

16. Pizza Dough Recipe (Requirements)‏ 1. Gather Ingredients 2. Combine sugar (1tbs), salt (1tbs), olive oil (1tbs), flour (1c) in mixing bowl 3. Turn on mixer 4. Add 1/4 cup of flour 5. If dough comes off the sides go to step 6, otherwise go back to step 4 6. Knead 15 minutes 7. Let rest for at least 45 minutes in warm area • 1 dough ball

17. N-Pizza Dough Program • Gather Ingredients • Combine sugar (N tbs), salt (N tbs), olive oil (N tbs), flour (N c) in mixing bowl • Turn on mixer • Add N/4 cup of flour • If dough comes off the sides go to step 6, otherwise go back to step 4 • Knead 15 minutes • Let rest for at least 45 minutes in warm area • N dough balls

18. N-Pizza Dough Program • Gather Ingredients • Combine sugar (N tbs), salt (N tbs), olive oil (N tbs), flour (N c) in mixing bowl • Turn on mixer • Add N/4 cup of flour • If dough comes off the sides go to step 6, otherwise go back to step 4 • Knead 15 minutes • Let rest for at least 45 minutes in warm area Sequence of Statements • N dough balls

19. N-Pizza Dough Program Variable • Gather Ingredients • Combine sugar (N tbs), salt (N tbs), olive oil (N tbs), flour (N c) in mixing bowl • Turn on mixer • Add N/4 cup of flour • If dough comes off the sides go to step 6, otherwise go back to step 4 • Knead 15 minutes • Let rest for at least 45 minutes in warm area • N dough balls

20. N-Pizza Dough - Program • Gather Ingredients • Combine sugar (N tbs), salt (N tbs), olive oil (N tbs), flour (N c) in mixing bowl • Turn on mixer • Add N/4 cup of flour • If dough comes off the sides go to step 6, otherwise go back to step 4 • Knead 15 minutes • Let rest for at least 45 minutes in warm area Conditional

21. N-Pizza Dough - Program • Gather Ingredients • Combine sugar (N tbs), salt (N tbs), olive oil (N tbs), flour (N c) in mixing bowl • Turn on mixer • Add N/4 cup of flour • If dough comes off the sides go to step 6, otherwise go back to step 4 • Knead 15 minutes • Let rest for at least 45 minutes in warm area Subroutines Mini-programs • N dough balls

22. Programming Languages • There are hundreds of different programming languages. • A few basic types of instructions appear in all of them • Input (get input from the user) • Output (display data to the user on a monitor or printout) • Math (perform basic mathematical operations) • Conditional Execution (check for conditions and execute the appropriate sequence of statements) • Repetition (perform some sequences of statements repeatedly) • Not too bad, right?

23. Programming Benefits • What do students learn through programming? • Mathematical and computational ideas • Coordinates, Variables, Random Numbers • Problem solving skills • Process of Design • Idea->Prototype->Experiments->Debugging->Redesign->New Ideas • Fluency with Digital Technology • To be fluent in language, you learn to read AND write – how to express yourself in the language. The same is true of programming – using the computer not just to interact but to create.

24. Debugging • Nobody’s perfect – especially not the first time! • Debugging is the process of finding errors in the program and correcting them. • The term was first used by Grace Hopper, when she found a “bug” in the computer in the 1950’s (see photo) • Debugging is a vital programming skill 1st use of “computer bug”

25. Types of Bugs • Syntax • Runtime • Semantic

26. Syntax Errors • Programs must have correct syntax in order to run. • Syntax refers to the structure of a program and the rules about that structure. • Just one syntax error caused your program to quit. • Be prepared for this to happen quite frequently at first!

27. Runtime Errors • An error that doesn’t appear until a program is run. • Aka “Exceptions”

28. Semantic Errors • Really difficult to find • Program runs to completion, but produces an incorrect result • Must find them by looking at what the code is doing, not what you think its doing.

29. Languages • Formal • Natural

30. Similarities between Natural and Formal Languages • Both have rules of syntax • Both can be parsed

31. Differences between Formal and Natural Languages • Ambiguity • Redundancy • Literalness

32. The First Program • “Hello World” • >>>print "Hello, World!" • This is an example of a print statement, which doesn’t actually print anything on paper. It displays a value on the screen. • The quotation marks in the program mark the beginning and end of the value; they don’t appear in the result.