CS1150 Principles of Computer Science Introduction (Part II)

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1 Principles f Cmputer Science Intrductin (Part II) Yanyan Zhuang Department f Cmputer Science UC. Clrad Springs

2 Review Terminlgy Class } Every Java prgram must have at least 1 class (same name as Java file) Methd } Java prgrams cntains a special methd called main public static vid main (String[] args) {..} The main methd is where a Java prgram starts executin Statements } Statements represent actins } Statements must end with a ; UC. Clrad Springs

3 Review Terminlgy Reserved wrds (keywrds) } Wrds that have specific meaning/cannt be used fr ther purpses } public, class, byte, int, lng, flat, duble, Blcks } Class blck and methd blck, using {} Cmments } // This is a line f cmment } /* This cmment can span acrss several lines */ UC. Clrad Springs

4 Review Identifier A name chsen by the prgrammer fr: classes, methds, variables, and cnstants Can start with letter, _ r $ (_ and $ are nt used much) UC. Clrad Springs

5 Overview Numerical Data Types Variables and cnstants Packages Data frmatting Data casting UC. Clrad Springs

6 Numerical Data Types Name Range Strage Size byte 2 7 t (-128 t 127) 8-bit signed shrt 2 15 t ( t 32767) 16-bit signed int 2 31 t ( t ) 32-bit signed lng 2 63 t bit signed (i.e., t ) flat Negative range: 32-bit flating pint E+38 t -1.4E-45 Psitive range: 1.4E-45 t E+38 duble Negative range: 64-bit flating pint E+308 t -4.9E-324 Reading fr primitive data types: Psitive range: 4.9E-324 t E UC. Clrad Springs

7 Numeric Operatrs Name Meaning Example Result + Additin Subtractin * Multiplicatin 300 * / Divisin 1.0 / % Remainder 20 % 3 2 UC. Clrad Springs

8 Integer Divisin +, -, *, /, and % 5 / 2 yields an integer / 2 yields a duble value % 2 yields 1 (the remainder f the divisin) ften called mdularperatin UC. Clrad Springs

9 Remainder Operatr % Remainder is very useful in prgramming Fr example, an even number % 2 is always 0 and an dd number % 2 is always 1 S yu can use this prperty t determine whether a number is even r dd Example: CmputeExpressin.java System.ut.println() prints nly strings, but cnverts number t string t print UC. Clrad Springs

10 Java Identifiers An identifier Rule } A sequence f characters that cnsist f letters, digits, underscres (_), and dllar signs ($), NO SPACES } Must start with a letter, _ r $, CANNOT start with a digit } CANNOT be a reserved wrd, true, false, r null } Can be f any length Example } Class/methd/variable/cnstant name (can refer by name later) Cnventin } Class names start with an upper case letter, variable/methd names start with a lwer case letter, cnstants all caps UC. Clrad Springs

11 Variables and Cnstants Variable Used t stre a value that may change E.g., duble length; length = 3.5; //length can change duble length = 3.5; // an (almst) equivalent way as abve Hw t use: Declare à assign a value à d smething t it } A variable can nly be declared nce } A variable must have a value (be initialized) befre we use it } Can mdify their value, display their value, use them in frmulas } Example: Arithmetic.java (hw t declare/use variables) UC. Clrad Springs

12 Variables and Cnstants Cnstant Used t stre a value that will NEVER change Cnstants fllw certain rules } Must have a name (a meaningful name, like variables) With all uppercase letters (Java cnventin) } Declared using the keywrd final Example: final duble PI = ; UC. Clrad Springs

13 Write pseudcde Nt real cde, but help rganize prgram lgic Can use a mix f prgramming language + natural language Example: Calculate the area f a circle (Circle.java) Input: radius Output: area f the circle area = pi * radius * radius Print area Als see Rectangle.java UC. Clrad Springs

14 Reading Input frm the Cnsle 1. Create a Scanner bject Scanner keybard = new Scanner(System.in); 2. Use the methd nextduble() t btain t a duble value. Fr example, System.ut.print("Enter a duble value:"); duble d = keybard.nextduble(); 3. After finishing the Scanner bject, clse it keybard.clse(); UC. Clrad Springs

15 Reading Input frm the Cnsle Scanner keybard = new Scanner(System.in); int value = keybard.nextint(); Example: Average.java, CmputeArea1.java, CmputeArea2.java Methd nextbyte() nextshrt() nextint() nextlng() nextflat() Descriptin reads an integer f the byte type. reads an integer f the shrt type. reads an integer f the int type. reads an integer f the lng type. reads a number f the flat type. nextduble() reads a number f the duble type. UC. Clrad Springs

16 Packages A bunch f related classes gruped tgether Mechanism fr rganizing Java classes Java cntains many predefined packages T access class/methd in a predefined package use imprt imprt java.util.scanner; UC. Clrad Springs

17 Packages T create yur wn package File (with prject selected) à New à Package First line in yur Java class: package yur_package_name Cnventin: package name lwer case Structure A prject cntains package(s) A package cntains Java file(s) A Java file cntains class(es) UC. Clrad Springs

18 Let s Practice! Please write a prgram CmputeRadius.java: input the area f a circle, calculate its radius Write pseudcde t guide yur lgic Use cnstant PI Use Scanner t get input value area (a duble variable) Print the value f the radius } radius = the square rt f (area/pi) } Hw t d square rt? Math.sqrt(area/PI) yu will use this in a hmewrk questin UC. Clrad Springs

19 Prblem: Cnverting Temperatures Write a prgram that cnverts a Fahrenheit degree (read frm keybard) t Celsius using the frmula: celsius 5 = ( 9 )( fahrenheit - 32) Print the resulting Celsius with tw decimal pints. 19

20 Cnverting Temperatures Pseudcde Input? Output? Hw t calculate Celsius given a Fahrenheit value? celsius 5 = ( 9 )( fahrenheit - 32) Nte: yu have t write celsius = (5.0 / 9) * (fahrenheit 32) Hw t print the result using tw decimal pints? } Data frmatting UC. Clrad Springs

21 Frmatting decimal utput Use DecimalFrmat class imprt java.text.decimalfrmat; DecimalFrmat df = new DecimalFrmat("000.##"); System.ut.println(df.frmat(celsius)); 0: a digit #: a digit, zer shws as absent } 72.5 is shwn as } is shwn as Mre infrmatin UC. Clrad Springs

22 Frmatting decimal utput Use System.ut.frmat System.ut.frmat("the %s jumped ver the %s, %d times", "cw", "mn", 2); } the cw jumped ver the mn, 2 times System.ut.frmat("%.1f", ); } 10.3 // ne decimal pint System.ut.frmat("%.2f", ); } // tw decimal pints System.ut.frmat("%8.2f", ); } // Eight-wide, twdecimal pints UC. Clrad Springs

23 Let s Practice! Please write a prgram: given the radius f a circle, calculate its perimeter, and print the result with 4 decimal pints Write pseudcde t guide yur lgic Use cnstant PI Use Scanner t get input value radius Print the value f the perimeter UC. Clrad Springs

24 Data Casting When yu explicitly tell Java t cnvert a variable frm ne data type t anther type Think f data types as cups f different sizes } Can put the cntents f a smaller variable (cup) int a larger variable (cup) } Cannt put the cntents frm a larger variable (cup) int a smaller variable (cup), withut lsing infrmatin } Cheat sheet: int (32 bits), lng (64 bits), flat (32 bits), duble (64 bits) UC. Clrad Springs

25 Cnversin Rules When perfrming a binary peratin invlving tw perands f different types, Java autmatically cnverts the perand based n the fllwing rules: 1. If ne f the perands is duble, the ther is cnverted int duble. 2. Otherwise, if ne f the perands is flat, the ther is cnverted int flat. 3. Otherwise, if ne f the perands is lng, the ther is cnverted int lng. 4. Otherwise, bth perands are cnverted int int. 25

CS1150 Principles of Computer Science Midterm Review

CS1150 Principles of Computer Science Midterm Review CS1150 Principles f Cmputer Science Midterm Review Yanyan Zhuang Department f Cmputer Science http://www.cs.uccs.edu/~yzhuang CS1150 UC. Clrad Springs Office hurs 10/15, Mnday, 12:05 12:50pm 10/17, Wednesday