Introduction to Computer Programming

1. Introduction to Computer Programming Pre-AP Computer Science, Cycle 5

2. Language of a Computer • Computers are electronic devices; they work by sending electronic signals • Electronic signals represent information in binary, using 0’s and 1’s • This binary language is called machine language • A single 0 or 1 is called a bit of data • Bit = binary digit • A sequence of 0’s and 1’s is called binary code

3. Bytes? • A sequence of 8 bits = 1 byte 10011101 • Kilobyte (KB)  1024 bytes • Megabyte (MB)  1024 KB • Gigabyte (GB)  1024 MB • Terabyte (TB)  1024 GB • Petabyte (PB)  1024 TB BIT BYTE

4. Binary into Letters • Binary code is translated into numbers, letters, and punctuation • Most common system: ASCII • American Standard Code for Information Interchange • 7 bits, or 128 different characters • ‘A’  1000001 • Another common system: Unicode • 16 bits, or 65,536 different characters • Useful for languages other than English • ‘A’  0000000001000001

5. Evolution of Programming Languages wages = rate * hours • Machine Code 100100 010001 100110 010010 storage locations 100010 010011 math operations • Assembly Language LOAD rate MULT hours STOR wages • High-level Language (C++, Java, Python, etc) wages = rate * hours;

6. Translating High-Level Languages to Machine Code • Remember, computers only understand machine code • Any other code must be translated back to machine code in order for the computer to execute the program

7. Translating to Machine Code

8. Java Compiler and IDE • Compiler (JDK 7) • http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html • Accept the license agreement • Download Java SE Development Kit 7u51 for Windows x64 (last one in the first table) • IDE/Editor (jGRASP) • http://spider.eng.auburn.edu/user-cgi/grasp/grasp.pl?;dl=download_jgrasp.html • Scroll down, then download/install jGRASP 2.0.0_07 for Windows

9. Test your Compiler public class MyFirstJavaProgram { public static void main(String[] args) { System.out.println(“Hello world!”); } } • Run the code by clicking on the red running man

10. Warm-up: February 18th • Why do you need to translate high-level programming languages into machine language? • Why would you prefer to write a program in a high-level programming language rather than a machine language?

11. Programming is Problem Solving PAP Computer Science, Cycle 5

12. Programming is Problem Solving • Most computer programs set out to solve a problem • Programming well requires good problem-solving skills • Problem-solving skills can be developed through various techniques

13. Algorithm Development • Analyze the problem • Really understand what it’s asking for • Outline the project requirements • What information do I need to bring in? • What information needs to be stored? • What information needs to be outputted? • Design your algorithm • Implement the algorithm • Verify the algorithm (test it) • Maintain and improve program

14. Algorithm: Perimeter and Area of a Rectangle Formulas: perimeter = 2*(length+width) area = length * width • Get the length of the rectangle • Get the width of the rectangle • Find the perimeter using the perimeter equation • Find the area using the area equation • Output the length, width, perimeter, and area of the rectangle

15. Computers are stupid! • They only do EXACTLY what you tell them to do • They take NO information for granted • They do not make assumptions • They do not automatically fill in gaps in instructions • They do not stop unless told to do so • EVERY step must be outlined for them

16. Demonstration: Robot Ms. Alexander • Take out a sheet of paper • On the paper, write the steps necessary for Ms. Alexander to walk from the door to her chair and sit down • Robot Ms. Alexander only knows how to take steps, bend her knees, and turn

17. Algorithm: Number-Guessing Game • The computer picks a randomly generate number between 1 and 100 • The user tries to guess the number • If the user’s guess is smaller than the number, the computer says “too small, guess again” • If the user’s guess is larger than the number, the computer says “too large, guess again” • The process repeats until the user guesses the correct number

18. Algorithm: Number-Guessing Game • Generate a random number • Save the random number in a variable called num • Repeat the following steps until the player has guessed the correct number: • Prompt the user to enter a guess • If guess = num, print “correct!” • Otherwise, if guess < num, print “Too small! Guess again!” • Otherwise, if guess > num, print “Too large! Guess again!”

19. Structured Programming • Divide larger, more complex programming problems into smaller, more manageable problems • Write code to solve the smaller problems, then use those answers to solve the large problem • Also called top-down design, bottom-up design, stepwise refinement, and modular design

20. Example: Programming a TV Remote Problem: We want to control a TV using a remote with many different buttons Number keys code Volume keys code Channel keys code

21. Object-Oriented Programming • Analyze a problem to determine what the major components are, and create objects to represent these components • Determine how these objects should be characterized, and how they should interact with each other • Each object is given characteristics (properties) • Each object is given abilities (methods)

22. Example: Video Game Rentals • Two main objects: video game and the customer • Video game object • Data: title, genre, rating, # in stock, price • Operations: be scanned, inc/dec stock as copies are rented/returned, be shelved • Customer object • Data: age, gender, renting history • Operations: rent a game, return a game, browse, search by…

23. Structured vs OOP • Structured • Better for mathematical functions • Better for simple, single-step, or few-step problems • Object-Oriented • Better for more complicated problems • Better for problems that use large amounts of related information • C, COBOL, FORTRAN, BASIC  structured programming languages • C++, Java, Ruby, Python, Perl  OOP programming languages

24. Warm-up: February 19 • Develop an algorithm for the following problem: Find the radius of a circle given the circle’s circumference. Formula: circumference = 2*pi*radius

25. Warm-up: February 19 • Develop an algorithm for the following problem: Find the radius of a circle given the circle’s circumference. Formula: circumference = 2*pi*radius • Input the circumference and save in a variable • Calculate radius by dividing the circumference by (2*3.141) • Output the radius

26. Basic Elements of a Java Program PAP Computer Science, Cycle 5

27. Example Code //***************************************** // Author: Rachel Alexander Date: 2/19/14 // This code displays three lines of text //***************************************** public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“Happy Wednesday!”); System.out.println(“Sum of 2 and 3 = “ + 5); System.out.println(“7 + 8 = “ + (7+8)); } }

28. Comments //***************************************** // Author: Rachel Alexander Date: 2/19/14 // This code displays three lines of text //***************************************** public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“Happy Wednesday!”); System.out.println(“Sum of 2 and 3 = “ + 5); System.out.println(“7 + 8 = “ + (7+8)); } }

29. Comments • It’s good programming practice to begin each code you write with a comment listing the author of the program, the data last modified, and a short description of what the code does • You should also comment key statements in a program • Single line comments: //This is a comment • Multi-line comments: /* This comment can span many lines. */

30. Classes //***************************************** // Author: Rachel Alexander Date: 2/19/14 // This code displays three lines of text //***************************************** public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“Happy Wednesday!”); System.out.println(“Sum of 2 and 3 = “ + 5); System.out.println(“7 + 8 = “ + (7+8)); } }

31. Classes • Classes are how we create objects in Java • Recall, Java is an object-oriented programming language • Each code we write must exist inside of a class • This class we named ASimpleJavaProgram • Public vs private classes will be discussed later

32. Methods //***************************************** // Author: Rachel Alexander Date: 2/19/14 // This code displays three lines of text //***************************************** public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“Happy Wednesday!”); System.out.println(“Sum of 2 and 3 = “ + 5); System.out.println(“7 + 8 = “ + (7+8)); } }

33. Methods • Code within classes must be written inside of a method • Methods are what cause actions to be performed in our Java code • Each class can only have one “main” method, but unlimited amounts of other named methods

34. Example Code //***************************************** // Author: Rachel Alexander Date: 2/19/14 // This code displays three lines of text //***************************************** public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“Happy Wednesday!”); System.out.println(“Sum of 2 and 3 = “ + 5); System.out.println(“7 + 8 = “ + (7+8)); } }

35. Output • System.out.println( ) is used to output information to the user • You can output text, variables, lists, or even math Example: System.out.println(“Happy Wednesday!”); Happy Wednesday!

36. Output • You can output mutiple types of expressions in one line by combining them with the ‘+’ operator Example: System.out.println(“The sum of 2 and 3 = “ + 5 ); The sum of 2 and 3 = 5 Example: System.out.println(“7 + 8 = “ + (7 + 8)); 7 + 8 = 15

37. Your Turn! Write a program that produces the following output: ****************************** * Programming Assignment 1 * * PAP Computer Science * * Author: YOUR NAME * * Date: February 19, 2014 * ****************************** CODE TEMPLATE: public classASimpleJavaProgram { public static void main(String[] args) { System.out.println(“TEXT GOES HERE”); } }

38. Warm-up: Thursday, Feb 20 • Name one way in which commenting code can be helpful. • What is the command for generating output?

39. Warm-up: Thursday, Feb 20 • Name one way in which commenting code can be helpful. • Notes/reminders to yourself and others • Declare the author of the code/date last modified • Explain key lines of code • What is the command for generating output? • System.out.println( )

40. Warm-Up: Friday, Feb 21 • Correct the 6 errors in the following code: public CLASS warmup { public static void main(String[] args) { System.Out.PrintIN(“Hello!) } }

41. Warm-Up: Friday, Feb 21 • Correct the 6 errors in the following code: public classwarmup { public static void main(String[] args) { System.out.println(“Hello!”); } }

42. Advanced Output Pre-AP Computer Science, Cycle 5

43. Recall… • Output is performed using the System.out.println() command • Example: System.out.println(“Hello world!”); • However, this is not the only command for output

44. Output Expressions • System.out.println( ) • Outputs onto a new line • System.out.print( ) • Outputs on the same line • System.out.printf( ) • Outputs with special formatting rules

45. Printlnvs Print System.out.println(“Hello”); System.out.println(“there.”); Hello there. System.out.print(“Hello”); System.out.print(“there.”); Hello there.

46. Outputting Different Data Types • Strings are enclosed in double quotes. • System.out.println(“Hello!”); • Characters are enclosed in single quotes • System.out.println(‘A’); • Numbers/variables are not enclosed in quotes • System.out.println(7); • System.out.println(4 + 12); • System.out.println(answer);

47. White Spaces • Typically, Java ignores “white spaces” • Spaces • Enters • Tabs • When outputting, some “white spacing” is allowed, while others are not allowed.

48. White Spaces System.out.print(“It’s sunny.”); System.out.println(“Let’s go outside.”); It’s sunny. Let’s go outside. System.out.println(“It’s sunny.” + “Let’s go outside.”); It’s sunny. Let’s go outside. System.out.println(“It’s sunny. Let’s go outside.”); ERROR MESSAGE

49. Escape Sequences • Escape sequences are used to output typically reserved characters • Slashes • “Enters” • Quotations • Tab • Escape sequences always begin with a forward slash (\) • This is found ABOVE THE ENTER KEY

50. Common Escape Sequences