CMSC 150 Introduction TO Computing

CMSC 150INTRODUCTION

TOCOMPUTING

CS 150: Fri 13 Jan 2012

Variable Declarations Use to request space in RAM to store

values Syntax: type variableName;

Types: int : whole number (e.g., 0, 1, 100,

1234) double : real-valued number (e.g.,

3.14159) char : one character (e.g., ‘A’, ‘9’,

‘q’) boolean : true or false String : character sequence (e.g.,

“Jason”)







“Jason”)

primitive types







“Jason”)

class type



Examples : int numberOfVictims; double minutesUntilDemise; char jasonsFirstInitial; boolean isKevinBaconStillAlive; String finalPleaForMercy;

In RAM

int numberOfVictims;double minutesUntilDemise;char jasonsFirstInitial;boolean isKevinBaconStillAlive;String finalPleaForMercy;

numberOfVictims

minutesUntilDemise

jasonsFirstInitial

isKevinBaconStillAlive

finalPleaForMercy

your programin memory

Assignment Statements Use to put values into variables Syntax: variableName = expression;

Examples : numberOfVictims = 13; minutesUntilDemise = 2.1; jasonsFirstInitial = ‘J’; isKevinBaconStillAlive = false; finalPleaForMercy = “Help Me!”;

literals(type must

match variable

type)

In RAM

numberOfVictims = 13; minutesUntilDemise = 2.1; jasonsFirstInitial = ‘J’; isKevinBaconStillAlive = false; finalPleaForMercy = “Help Me!”

numberOfVictims

minutesUntilDemise

jasonsFirstInitial

isKevinBaconStillAlive

finalPleaForMercy

your programin memory

13

2.1

J

false

Help Me!

Declaration + Assignment Combine into a single statement Syntax: type variableName =

expression;

Examples : int numberOfVictims = 13; double minutesUntilDemise = 2.1; char jasonsFirstInitial = ‘J’; boolean isKevinBaconStillAlive = false; String finalPleaForMercy = “Help Me!”;

Assignments & ExpressionsnumberOfVictims = 13;

numberOfVictims = numberOfVictims + 1;evaluate right-hand

side

value: 13

numberOfVictims

minutesUntilDemise


numberOfVictims = numberOfVictims + 1;

13

numberOfVictims

minutesUntilDemise

13



numberOfVictims

minutesUntilDemise

evaluate right-hand side

value: 13 + 113



14

numberOfVictims

minutesUntilDemise

14


numberOfVictims = numberOfVictims + 1;numberOfVictims = numberOfVictims + 7; // party!

numberOfVictims

minutesUntilDemise

evaluate right-hand side

value: 14 + 7 14


numberOfVictims = numberOfVictims + 1;numberOfVictims = numberOfVictims + 7; // party!

21numberOfVictims

minutesUntilDemise

21

Incrementing Increment : add one to a variable

Three ways: numberOfVictims = numberOfVictims + 1; numberOfVictims += 1; numberOfVictims++;

All result in value increasing by one

Expressions Numerical operators:

+ − * / %

Examples of expressions: 3.14159 + 2 (11 – 3) * 4 2 / 4 2.0 / 4 4 % 3 m * (c * c)

Expressions Numerical operators:

+ − * / %

Examples of expressions (with variables): double piPlusTwo = 3.14159 + 2; double thirtyTwo = (11 – 3) * 4; double zero = 2 / 4; double oneHalf = 2.0 / 4; double remainder = 4 % 3; double e = m * (c * c);

Expression takes on type of largest-storage operand in expression

Examples of expressions (with variables): double piPlusTwo = 3.14159 + 2; double thirtyTwo = (11 – 3) * 4; double zero = 2 / 4; double oneHalf = 2.0 / 4; double remainder = 4 % 3; double e = m * (c * c);

Expression Type

Division Works differently for integers vs.

floating-point

Examples: 8.0 / 3.0 gives true floating-point result

8 / 3 gives integer quotient

8 % 3 gives integer remainder

Be Wary double myShare = (1/2) * inheritance;

double onePointSixRepeat = (double)(5 / 3);

double threeFifths = 3/5; double wormHole = someValue / threeFifths;

Strings & String Methods String homerSez = “Donuts. Is there anything they can’t do?”; 0123456789112345678921234567893123456789 0 0 0

int quoteLength = homerSez.length();// 40 char firstChar = homerSez.charAt( 0 ); // ‘D’ char period = homerSez.charAt( 6 ); char questionMark = homerSez.charAt( 39 ); char eye = homerSez.charAt( homerSez.indexOf( ‘I’ ) );

String donutsCap = homerSez.substring(0, 6); // “Donuts” String donuts = donutCap.toLowerCase(); // “donuts”

String nuts = donuts.substring( 2 ); // 2 to end String nutsCubed = nuts + “ ” + nuts + “ ” + nuts + “!”;

Strings & String Methods String homerSez = “Donuts. Is there anything they can’t do?”; 0123456789112345678921234567893123456789 0 0 0 int quoteLength = homerSez.length();// 40 char firstChar = homerSez.charAt( 0 ); // ‘D’ char period = homerSez.charAt( 6 ); char questionMark = homerSez.charAt( 39 ); char eye = homerSez.charAt( homerSez.indexOf( ‘I’ ) );

String donutsCap = homerSez.substring(0, 6); // “Donuts” String donuts = donutCap.toLowerCase(); // “donuts”

String nuts = donuts.substring( 2 ); // 2 to end String nutsCubed = nuts + “ ” + nuts + “ ” + nuts + “!”;

Digits int one = 1; char uno = ‘1’; String ein = “1”;

All are different Only one contains the integer value 1

1 + 1 // 2 ‘1’ + ‘1’ // 98 (more on this later) “1” + “1” // “11”

Comments Allow you to annotate your programs Two options:

inline // this is an example of an inline comment

block /* this is an example of a block comment */

Java does not execute comments

Use to describe (in English) what your code does

Also use to (temporarily) disable parts of code

public class ClassWithComments

{

public static void main( String[] args )

{

int numberOfVictims = 13; // number of people Jason has greeted

double minutesToDemise = 2.1; // mins from start of movie to 1st death

// Jason just met another person, so add one to # of victims


// Jason crashed a party, so really bump the victim count


/*

Let’s comment out the Kevin Bacon code for now...

Turns out that was just a dream sequence, but we might need

this code later!

// Jason killed Kevin Bacon’s character


*/

…

// Author: Kyra Sedgwick (you may need to search for the reference…)

// Date: 13 Friday 2012

// Purpose: This program keeps count of the number of victims of the

// “protagonist” Jason from the slasher movie “Friday The 13th”,

// along with some other interesting movie trivia.


{


{







…

/* Author: Kyra Sedgwick

Date: 13 Friday 2012

Purpose: This program keeps count of the number of victims of the

“protagonist” Jason from the slasher movie “Friday The 13th”,

along with some other interesting movie trivia.

*/


{


{







…

CMSC 150 Introduction TO Computing

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