Module2- Part1

Variables,Assignment,andDataTypes

1/23/19 CSE1321MODULE2 1

MotivationTolearnthebasicelementsofprogramming:

1. Declaringvariables(anamedchunkofmemory)

2. Datatypes(thekindofinfoyou’regoingtostore)

3. Assignment(puttingvaluesintoachunkofmemory)

4. Stringliterals

5. Reviewprinting

1/23/19 CSE 1321 MODULE 2 2

Topics

1.ProgramStructure2.CharacterStrings3.Variables4.Assignments5.Constants6.PrimitiveDataTypes

1/23/19 CSE 1321 MODULE 2 3

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AnapplicationalwayscontainsaMAINmethodsothattheprogramcanbeexecuted.

Inobject-orientedprogramming(OOP)language,MAIN isinsidea“class”

Theseprogramelementstermswillbeexploredindetailthroughoutthecourse

ProgramStructure

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Commentsarejustnotes thatexplaintheprogramtoyourselfandothers.They’reGREEN!

BlockcommentsinJavaandC#◦ Beginwith/*andendswith*/◦ Compilerignoresalltextbetween/*and*/◦ Singlelinecommentsstartwith//◦ Compilerignorestextfrom //toendofline

BlockcommentsinPython◦ Single-linecommentsusethehash(#)character◦ Commentsthatspanmultiple linesarecreatedbyaddingadelimiter(“””)oneachendofthecomment.

Comments

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Anidentifierisjustanameyougive avariable

Rulesfornames:◦ C#:Muststartwithaletter,cancontainessentiallyanynumberoflettersanddigits,butnospaces,casesensitive.Itcannotbekeywordsorreservedwords– whichturnblue!

◦ Java:Muststartswithaletter,anunderscore(_),oradollarsign($).Cannotstartwithadigit.Cannotbeakeywords(whichturnblue).Canbeofanylength.Casesensitive.

◦ Python:MuststartswithaletterAtoZoratozoranunderscore(_)followedbyzeroormoreletters,underscoresanddigits(0to9).

Identifiers

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abstract assert boolean break byte case catch char class const continue default do double else enum extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while

JavaKeywords(badforvariablenames)

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abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in intinterface internal is lock long namespace new null object operator out override paramsprivate protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushortusing var virtual void volatile while

C#Keywords(badforvariablenames)

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False def if raise None del import return True elif in try and else is while as except lambda with assert finally nonlocal yield break for not class from or continue global pass

PythonKeywords

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Spaces,blanklines,andtabsarecalledwhitespace:

1. Usedtoseparatewords andsymbolsinaprogram.Extrawhitespaceisignored

2. Avalidprogramsyntaxcanbeformattedmanyways

3. Usewhitespaceenhancereadability,usingconsistentindentation

WhiteSpace

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A“stringliteral”contains0ormorecharactersenclosedwithdoublequotes(inJavaandC#)orsinglequotes(inPython).They’reRED.Examples:◦ “Thequickbrownfoxjumped.”(JavaandC#)◦ 'Thequickbrownfoxjumped.'(Python)◦ “x”(JavaandC#)◦ 'x'(Python)

Squarebrackets[]canbeusedtoaccesselementsinsidethestring(later)

CharacterStrings

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System.out.println (“Whatever you are, be a good one.”);

1. SystemrepresentstheOperatingSystem

2. “out”istheconsole/screendatastream

3. println isa“function”topushdatatotheconsole

PrintingstringsinJava(review)

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Console.WriteLine (“Whatever you are, be a good one.”);

1. ConsolerepresentstheOperatingSystem’sconsole

2. WriteLine isa“function”topushdatatotheconsole

PrintingstringsinC#(review)

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print (‘Whatever you are, be a good one.’)

1. It’sjustprint!

PrintingstringsinPython(review)

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StringliteralscannotspanmultiplelinesCombinesstringliteralswithotherdatatypesforprintingExample(C#):

String hello = "Hello";String there = "there";String greeting = hello + ' ' + there;Console.WriteLine(greeting );

◦ Output:Hellothere

StringConcatenationOperator(+)

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CLASS CountDown BEGIN METHOD Main()BEGIN s1 ← "Three... "s2 ← "Two... " s3 ← "One... "s4 ← "Zero... "PRINT(s1 + s2 + s3 + s4 + "Liftoff!") PRINTLINE()

PRINT("Houston, we have a problem.") END Main

END CountDown

Output:

Three... Two... One... Zero... Liftoff!Houston, we have a problem.

Pseudocode

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// Program CountDown.java

public class CountDown {

public static void main (String[] args) {

String s1 = "Three... "; String s2 = "Two... "; String s3 = "One... "; String s4 = "Zero... "; System.out.println (s1 + s2 + s3 + s4 + "Liftoff!"); System.out.println ("Houston, we have a problem.");

} }

Output:

Three... Two... One... Zero... Liftoff!Houston, we have a problem.

Java

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using System;class CountDown {

public static void Main(string[] args){

Console.Write("Three... ");Console.Write("Two... ");Console.Write("One... ");Console.Write("Zero... ");Console.WriteLine("Liftoff!"); //on first lineConsole.WriteLine("Houston, we have a problem. ");

}}

Output:Three... Two... One... Zero... Liftoff!Houston, we have a problem.

C#

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def main():s1='Three... 's2='Two...'s3='One... 's4='Zero... 'print (s1+s2+s3+s4+'Liftoff!')print()print ('Houston,wehaveaproblem.')

if__name__=='__main__':main()

Output:Three... Two... One... Zero... Liftoff!Houston, we have a problem.

Python

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Printingandescapesequence printsaspecialcharacterinanoutputstring.Commonescapesequences:◦ \b backspace.(e.g “B\bsecz\bret”printswhat?)◦ \t tab◦ \n newline◦ \r carriagereturn◦ \” doublequote◦ \’ singlequote◦ \\ backslash

EscapeSequences

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public class Roses {

public static void main (String[] args) {

System.out.println ("Roses are red,\n\tViolets are blue,\n"+ "Sugar is sweet,\n\tBut I have \"commitment issues\",\n\t"+ "So I'd rather just be friends\n\tAt this point in our "+ "relationship.");

}}Output:

Roses are red,Violets are blue,

Sugar is sweet,But I have "commitment issues",So I'd rather just be friendsAt this point in our relationship.

Java

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// Escape sequencesclass Roses{

public static void Main(string [] args){

Console.WriteLine("Roses are red,\n\tViolets are blue,\n" + "Sugar is sweet,\n\tBut I have " + "\"commitment issues\",\n\t" + "So I'd rather just be friends\n\t" + "At this point in our relationship.");

}}

C#

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#Escapesequencesdef main():print ('Rosesarered,\n\tVioletsareblue,\n'+'Sugarissweet,\n\tButIhave\'commitmentissues\',\n\t'+'SoI\'dratherjustbefriends\n\tAtthispointinour'+'relationship.')

if__name__=='__main__':main()

Python

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Avariable isanameforalocationinmemoryusedtoholdadatavalue.Avariablemustbedeclaredbyspecifyingthevariable'sname andthetype ofinformationthatitwillhold.

Examples(JavaandC#):int total; // chunk of memory named totalint count, temp, result; // three variables

Multiplevariablescanbecreatedinonedeclaration

Variables

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// Prints the number of keys on a piano.CLASS PianoKeysBEGIN

METHOD Main()BEGINkeys ← 88PRINT("A piano has " + keys + " keys.")

END MainEND PianoKeys

Output: A piano has 88 keys.

Pseudocode

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// Prints the number of keys on a piano.public class PianoKeys{

public static void main (String[] args){

int keys = 88; //declare and initializeSystem.out.println ("A piano has " + keys + " keys.");

}}

Output: A piano has 88 keys.

Java

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// Prints the number of keys on a pianousing System;

class PianoKeys {public static void Main (string[] args) {

int keys = 88; //declare and initializeConsole.WriteLine("A piano has " + keys + " keys.");

}}

Output: A piano has 88 keys.

C#

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#prints the number of keys on a piano.

def main():keys = 88print("A piano has ", keys, " keys.");

if __name__ == '__main__':main()

Output: A piano has 88 keys.

Python

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Namesofvariables:◦ shouldbemeaningful◦ reflectthedata theywillstore.◦ variablenameswill“selfdocument”theprogram◦ smallvariablenamesareNOTmoreefficient◦ avoidextremelylongnames

Avoidnamessimilartokeywords

Conventions– NamingVariables

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Assignment statements change the value of a variable

The assignment operator is the = sign

total = 55; // put value of 55 into total

The expression on the right is evaluated and the result is stored in the variable on the left

The value that was in total is overwritten

The data type on the right must match the data type on the left!

Assignment

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// Print the number of sides of several geometric shapes.CLASS GeometryBEGIN

METHOD Main()BEGIN

sides ← 7PRINT("A heptagon has " + sides + " sides.")sides ← 10PRINT("A decagon has " + sides + " sides.")sides ← 12PRINT("A dodecagon has " + sides + " sides.")

END MainEND Geometry

Output:A heptagon has 7 sides.A decagon has 10 sides.A dodecagon has 12 sides.

Pseudocode

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// Print the number of sides of several geometric shapes.public class Geometry {

public static void main (String[] args) {int sides = 7; // declare and initializeSystem.out.println ("A heptagon has " + sides + " sides.");sides = 10; // assignment statementSystem.out.println ("A decagon has " + sides + " sides.");sides = 12; // assignment statementSystem.out.println ("A dodecagon has " + sides + " sides.");

}}

Java

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// Print the number of sides of several geometric shapes.using System;

class Geometry {public static void Main (string[] args) {

int sides = 7; // declare and initializeConsole.WriteLine("A heptagon has " + sides + " sides.");sides = 10; // assignment statementConsole.WriteLine("A decagon has " + sides + " sides.");sides = 12; // assignment statementConsole.WriteLine("A dodecagon has " + sides + " sides.");

}}

C#

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def main():sides=7#declareandinitializeprint("Aheptagonhas",sides,"sides.")sides=10#assignmentstatementprint("Adecagonhas",sides,"sides.")sides=12#assignmentstatementprint("Adodecagonhas ",sides,"sides.")

if __name__=='__main__':main()

Python

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Valuesthatcannotchange.

Avaluemustbeassignedbeforetheconstantisused.

Threereasons:◦ Theygivemeaningtootherwiseunclearliteralvalues.Forexample,MAX_LOADmeansmorethantheliteral250

◦ Programmaintenance.Ifaconstantisusedinmultipleplaces,itsvalueneedonlybeupdatedinoneplace.

◦ Avoiderrors byotherprogrammers

Constants

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UseallCAPITALLETTERSforconstantsandseparatewordswithanunderscore:

Forexample(Java):final double TAX_RATE = .05;

Declareconstantsatthetopoftheprogram

PythondoesnotsupportConstants.

Constants– JavaandC#

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Datatypetellscompiler:– Howmuchmemory toallocate– Format inwhichtostoredata– TypesofoperationsyouwillperformondataCompilermonitorsuseofdata– C#,Java,andPythonare"stronglytyped"language.Thatis,variablescannotbeimplicitlycoercedtounrelatedtypes

DataTypes

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• 8 simple data types:– 4 subsets of integers– 2 subsets of floating point numbers– Character– Boolean

• Everything else is a complex data type, built from simple or other complex data types

• Later, we’ll define our own data types!

DataTypes

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Differenceisinamountofmemoryreservedforeach(i.e thesizeofthevaluestored)1. Afloatonlyhas7significantdigits2. Signednumbershavebothpositiveandnegative

values3. Unsignednumbersare>=0

Whysomanytypes?

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Statictypechecking(C#andJava)•Statictypecheckingoccursduringcompilation•Requiresyoutodeclarevariabletypesbeforeyouusethem

Dynamictypechecking(Python)•Dynamictypecheckingoccurswhileprogramisrunning•Doesnot requireyoutodeclarethedatatypesofyourvariablesbeforeyouusethem

•Pythonusesdynamictyping,butisalsoisstronglytyped,astheinterpreterkeepstrackofallvariablestypes.

Staticv.DynamicTyping

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Values without a decimal point are considered int

Values with decimal point are considered double, which is bigger than a float!

Examples (Java)int testGrade = 100;byte ageInYears = 19;long cityPopulation = 425612340L float salesTax = .05F; // NOTE the Fdouble interestRate = 0.725; double avogadroNumber = +6.022E23;

LiteralNumbers

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Twocommonwaystoholdcharacters:1. ASCII(8bits)– howmanycharactersinEnglish?2. Unicode(16bits)– howmanycharactersinMandarin?3. Unicodeismostcommonlyused

Exampledeclarations:char finalGrade = ‘A’; // NOTE single quoteschar newline, tab, doubleQuotes;

PythonhasNOchardatatype.

char DataType(JavaandC#)

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Two values only:– true

– false

Used for decision making or as "flag" variablesExample declarations:bool isEmpty = false; //in C#boolean passed = true; //in JavaA = True //in Python

boolean DataType

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1. Variable declaration indicates its type and possibly its initial value.

2. A value is assigned using assignment operator.

3. A constant value doesn’t change

4. Data type tells how much memory to allocate, the format in which

to store data, and the types of operations you will perform on

data.

5. Primitive data types include integer, floating point, character,

boolean, and decimal.

Summary