CS 1101 Group 1 Discussion 1 Lek Hsiang

CS 1101 Group 1 Discussion 1 Lek Hsiang Hui lekhsian @ comp. nus. edu. sg http: //www. comp. nus. edu. sg/~lekhsian/cs 1101

Programming background?

Style of discussion • Discuss previous week lab • Discuss current week lab (good to read up the lab question before coming class) • Go through some concepts of materials cover during that week • Quiz • Mini “in-class” exercises

Other Issues • Please do NOT call me sir – I’m also a student! • Check your email regularly • Check out course website regularly • My cs 1101 website (for discussion notes and related materials) • Encourage you all to participate actively on the IVLE forum • At any point of time, you can ask question, please let me know whether I’m too soft, mumbling etc

Questions from lectures?

• Be passionate about programming • Find sources of practice – Try out codes in the textbook – Past yet cs 1101/c PE questions – google for more questions – http: //www. comp. nus. edu. sg/~cs 1101 x • Know the concepts – Look for a src. zip in your jdk folder System. out. println(“hello world”); is really System. out. print(“hello world”); new. Line();

• Nature of CS 1101 – This module can be very easy or very tough – Its not one module where you can do last min effort, in fact if you can follow, its one module where you can feel quite relax just before exams • Practice make perfect • Read before hand later topics – It’s difficult to relate a certain syntax to how its typically being used • Seek help if you are facing problem, don’t wait until test/exams then you start to panic

Java Programming Style / Convention

Java Programming Style /Convention • Please read through http: //www. comp. nus. edu. sg/~cs 1101/3_c a/labs/styleguide. html – – – Indentation Comment your code Classes should start with uppercase Variables should start with lowercase Methods should start with lowercase Final variables/constants should be all uppercase e. g final int PI = 3. 14;

Java Programming Style /Convention • Variable Names – Case-sensitive – Begins with a letter, dollar sign($) or underscore – White spaces are not permitted – Subsequent characters may be a letter, digit, dollar sign or underscore

CS 1101 Labs

CS 1101 Labs • !!! Very important - 20% • Make sure you indent your code – If you are using Dr Java, there’s a indentation feature, just select all your code and press Tab • Provide comments (in English please!) • Do early, email me early if you encounter problems • Do NOT copy from anyone! (changing variables names, spacing, shifting codes around is not going to work!)

Learn how to use the Java API • http: //java. sun. com/javase/6/docs/api/ – Go to google -> Search for java 1. 6 api -> Press I’m feeling Lucky • E. g Scanner sc = new Scanner(System. in); int I = sc. next. Int(); there’s also next. Double(), next. Float(), …

Learn how to use the Java API • Scanner – Import details : java. util. Scanner – Constructor new Scanner(…); – Methods return type and method name int : next. Int(); String : next. Line(); • Math

Numerical Data int - 32 bit 231 + (231 - 1) = 232 231 = -2147483648 231 - 1 = -2147483647

Question Q. What is the result of : System. out. println(011); 9 How do we get 9? 1 * 81 + 1 * 8 0 = 9 Octal (base 8)

Things you should know by now…

Primitive Data Types • • • boolean char int float double Did you know that char is actually of a integer type char a = 'A'; System. out. println(a + 0); //print 65 System. out. println((char)(a + 1)); //print B

Reserved Words • Reserved words cannot be used as identifiers (variables names)

Statements • Statements are code that must do something • Some typical statements you will see up to now: • Variable declaration int num; • Assignment statements num = 1; • Prefix / Postfix statements ++x; x--; etc • Method calls

Statements • Java also allow you to define blocks public static void main(String args[]){ { int num = 1; System. out. println(num); } int num = 2; System. out. println(num); } prints 1 2

Expressions • A set of codes that returns a value E. g (1 + 1) this piece of code returns/gives you a value of 2 • Could be something like System. out. println( Math. max(1, 2) );

Arithmetic Operators • +, -, * • / and % – These 2 operations are usually used when dealing with getting the digits of a number • Type promotions

Type Promotions Type Able to be promoted to double Not able to promote anymore. float double long float double int long float double char int long float double 1/2=0! short int long float double byte short int long float double boolean Not able to promote. 4 / 2. 0 = 2. 0 not 2

Casting Compilation • (<data type>) <expression> Error! • Q. What do you think is the output of public static void main(String args[]){ int a = 10; int b = (int) a / 2. 0; System. out. println(b); }

Increment & Decrement Operators Expression Operation x = ++y Pre-increment x = y++ Post-increment x = --y Pre-decrement x = y-- Post-decrement Q. What is the output of public static void main(String args[]){ int a = 1; System. out. println(a++); System. out. println(a); } 1 2

Increment & Decrement Operators Expression Operation x = ++y Pre-increment x = y++ Post-increment x = --y Pre-decrement x = y-- Post-decrement Q. What is the output of public static void main(String args[]){ int a = 1; System. out. println((a++) + (a++)); System. out. println(a); } 3 3

Increment & Decrement Operators Q. What is the output of public static void main(String args[]){ int a = 1; System. out. println((a++) + (a++)); System. out. println(a); } 1 A 2 1 3 2 3 3

Boolean Operations • && , ||, ! • Expressions with these operators are evaluated by “shortcircuit evaluation” • Or lazy evaluation i. e. expression not evaluation if we already know the results • e. g true || false (true or anything) -> true, so no point evaluating the 2 nd part Precedence Order Operator 1 () 2 ! 3 && 4 ||

Boolean Operations • more e. g false && true (false and anything) -> false, so no point evaluating the 2 nd part

Relational Operators • >, < • Op= operators >=, <= , ==, !=

Assignment Operator • • a= 1 + 3 Step by Step: a= (we now need to find a value which will be given to the LHS) • a=4

Assignment Operator • Try out with int a = 1; a = (a + (a = (a + 1))); • a = (1 + (a = (1 + 1))); • a = (1 + (a = 2)); //assign 2 to a and return value of a • a = (1 + 2); • a = 3;

Precedence and Associativity Operator Type Operator Precedence Level Associativity Unary []. (params) E++ E-- 1 Left to right Unary unary operators: -E !E ~E ++E --E 2 Right to left Object creation / Cast new (type)E 3 Right to left Arithmetic */% 4 Left to right Arithmetic +- 5 Left to right Bitwise >> << >>> 6 Left to right Relational < > <= >= 7 Left to right Relational == != 8 Left to right Bitwise & 9 Left to right Bitwise ^ 10 Left to right Bitwise | 11 Left to right Logical && 12 Left to right Logical || 13 Left to right Conditional ? : 14 Right to left Assignment = += -= *= /= %= >>= <<= &= ^= |= 15 Right to left