CS Week 2. Jim Williams

Transcription

1 CS Week 2 Jim Williams

2 This Week Team Labs Lecture: Scanner, data types, conditionals

3 Team Labs First meeting this week cs and 1370 cs Expect an Ice Breaker, be assigned a partner and do the lab together. Pair programming

4 Pair Programming 2 people working together on 1 computer. One person types, the other provides direction and reviews. Many report more confidence in solution and more enjoyment programming. Import to switch roles (who has the keyboard). Provide respectful, honest and friendly feedback

5 P1 - Review Quiz Available 3 weekly milestones, Due 8am Thursday First 2 milestones auto-graded Third milestone additional tests and human graded. P1 - Individual work Discuss concepts, don t share code Style and Commenting

6 Piazza notes Don't post your code publicly (working or not). You can post code from the book if you cite it. From section 2.3.1,... Review the other posts (search for common terms) before posting as your question may already have been answered. Refer to these posts along with your question and say how yours is different.

7 What are values of variables? String note = "Minsub\n22\nCS"; Scanner input = new Scanner( note); String name = input.nextline(); int age = input.nextint(); String major = input.nextline(); name: Minsub\n22\CS age: major: name: Minsub age: 22 major: name: Minsub age: 22 major: CS

8 What are values of variables? String note = "20 25\nscores"; Scanner input = new Scanner( note); int score1 = input.nextint(); int score2 = input.nextint(); String title = input.nextline(); score1: 20 score2: 25 title: scores score1: 20 score2: 25 title: score1: score2: scores title:

9 Number Systems Decimal 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 Binary 0, 1

10 Decimal = 302

11 Binary = 14 0

12 Binary = 5

13 Names for Numbers of Bits bit nibble (4 bits) byte (8 bits) 2 bytes (16)

14 Hexadecimal (group bits by nibble) 0000 = = = = = = = = = = = A 1011 = B 1100 = C 1101 = D 1110 = E 1111 = F

15 Characters = 0x0041 = 65 Unicode 0x003E 62 > 0x003F 63? 0x0040 0x A 0x B 0x C

16 Color Red, Green, Blue (RGB) 183, 1, 1 B

17 Primitive Data Types int whole numbers (4 bytes) double floating point numbers (8 bytes) char single character (2 bytes) boolean true or false value (>= 1 bit) less commonly used: float, long, short, byte

18 boolean operators (comparison) ==!= < <= > >= int n = 6; boolean result = (n!= 5); result: true result: false

19 Primitive vs Reference Data Types Primitive Store value Reference Store a reference to place in memory to find value

20 java.util.random Random randgen; //Declare reference variable randgen = new Random(); //create instance // randgen.setseed( 123); //set state int valuea = randgen.nextint( 5); //get a value int valueb = randgen.nextint( 5); int valuec = randgen.nextint( 5);

21 Calling String methods String stra = "This is a string"; char achar = stra.charat( 3); answer:true boolean answer; answer = achar == 'i'; answer:false

22 java.lang.string String stra = "This is a string"; //String literal int lengtha = stra.length(); int lengthb = "This is a string".length();

23 Values of a1 and a2? String str1 = "Hello"; String str2 = new String( "Hello"); boolean a1 = str1 == str2; boolean a2 = str1.equals(str2); a1: true a2: true a1: false a2: true a1: true a2: false a1: false a2: false

24 Values of a1 and a2? char ch1 = 'H'; String str = "Hello"; char ch2 = str.charat(0); boolean a1 = ch1 == ch2; boolean a2 = ch1.equals(ch2); a1: true a2: true a1: false a2: true a1: true a2: false a1: false a2: false

25 Calling java.lang.math methods double numints = Math.pow( 2, 32); double root = Math.sqrt( 16); int age1 = 5; int age2 = 25; double big = Math.max( age1, age2); double max( double a,double b) float max( float a, float b) int max(int a, int b)

26 Are these equivalent? boolean tired = true; if ( tired) { //take break tired = false; } if (!tired) { //keep working } boolean tired = true; if ( tired) { //take break tired = false; } else { //keep working } Different style, same result Different style, different result

27 Floating Down a River

28 Side Trip, maybe multiple side trips boolean tired = true; if ( tired) { System.out.println( take break ); }

29 One side of the Island or the other boolean sunny = false; if ( sunny) { System.out.print( sunny ); } else { System.out.print( not sunny ); } System.out.println( and back together );

30 Equivalent? char chr = //any valid char out = 'W'; if ( chr == 'A') { out = 'X'; } else if ( chr == 'B') { out = 'Y'; } else { out = 'Z'; } char chr = //any valid char out = 'W'; if ( chr == 'A') { out = 'X'; } if ( chr == 'B') { out = 'Y'; } if ( chr!= 'A' chr!= 'B') { out = 'Z'; } Yes No

31 Dangling Else - What is out? int value = 0; String out = "abc"; if ( value >= 1 ) { if ( value <= 10) out = "1 to 10"; } else out = "else"; out: abc out: 1 to 10 out: else out: abcelse

32 What is the value of msg? int count = 5; String msg = "count is 5."; if ( count!= 5 ); { msg = "count is not 5."; } count is 5. count is not 5. count is 5.count is not 5.