Operator & Expressions

8/6/2019 Operator & Expressions

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Modifying objects

Operators and Expressions

JPC and JWD 2002 McGraw-Hill, Inc.


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Memory Depiction

float y = 12.5;12.5y

1001100210031004


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Memory Depiction

float y = 12.5;

int Temperature = 2;12.5

2

y

Temperature

1001100210010041005

1006


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Memory Depiction

float y = 12.5;

int Temperature = 2;

char Letter = 'c';

12.5

2'c'

y

TemperatureLetter

1001100210010041005

10061007


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Memory Depiction

float y = 12.5;

int Temperature = 2;

char Letter = 'c';

int Number;

12.5

2'c'

y

TemperatureLetter

1 11 2111 5

11

-Number 1 81 9


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Definition

int NewStudents = ; NewStudents


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Definition

int NewStudents = ;

int OldStudents = 21; 21

NewStudents

OldStudents


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Definition

int NewStudents = ;

int OldStudents = 21;

int TotalStudents;

21

NewStudents

OldStudents

TotalStudents


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Assignment Statement

int NewStudents = ;


int TotalStudents;

TotalStudents = NewStudents + OldStudents;

21

NewStudents

OldStudents

?TotalStudents


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int NewStudents = ;


int TotalStudents;


21

NewStudents

OldStudents

2TotalStudents


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int NewStudents = ;


int TotalStudents;


OldStudents = TotalStudents;

?

NewStudents

OldStudents

2TotalStudents


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int NewStudents = ;


int TotalStudents;


OldStudents = TotalStudents;

2

NewStudents

OldStudents

2TotalStudents


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Consider

int Value1 = 1 ; 1Value1


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Consider

int Value1 = 1 ;

int Value2 = 2 ;

int Hold = Value1;

1

2

Value1

Value2

1Hold


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Consider

int Value1 = 1 ;

int Value2 = 2 ;

int Hold = Value1;

Value1 = Value2;

2

Value1

Value2

1Hold


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Consider

int Value1 = 1 ;

int Value2 = 2 ;

int Hold = Value1;

Value1 = Value2;

2

2

Value1

Value2

1Hold


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Consider

int Value1 = 1 ;

int Value2 = 2 ;

int Hold = Value1;

Value1 = Value2;

Value2 = Hold;

2Value1

Value2

1Hold


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Consider

int Value1 = 1 ;

int Value2 = 2 ;

int Hold = Value1;

Value1 = Value2;

Value2 = Hold;

We swapped the values of objects Value1 and Value2 usingHold as temporary holder for Value1s starting value!

2

1

Value1

Value2

1Hold


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Incrementing

int i = 1;i 1


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Const Definitions

Modifier const indicates that an object cannot be changed

Object is read-only

Useful when defining objects representing physical andmathematical constants

const float Pi = .1 15;

Value has a name that can be used throughout the program

const int SampleSize = 1 ;

Makes changing the constant easy

Only need to change the definition and recompile


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Assignment Conversions

Floating-point expression assigned to an integer object istruncated

Integer expression assigned to a floating-point object isconverted to a floating-point value

Consider

float y = 2. ;

int i = 15;

int j = 1 ;i = y; // i is now 2

cout


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Nonfundamental Types

Nonfundamental as they are additions to the language

C++ permits definition of new types and classes

A class is a special kind of type

Class objects typically have

Data members that represent attributes and values

Member functions for object inspection and manipulation

Members are accessed using the selection operator (.)

j = s.size(); Auxiliary functions for other behaviors

Libraries often provide special-purpose types and classes

Programmers can also define theirown types and classes


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Examples

Standard Template Library (STL) provides class string

EzWindows library provides several graphical types and classes

SimpleWindow is a class for creating and manipulatingwindow objects

RectangleShape is a class for creating and manipulating

rectangle objects


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Nonfundamental Types

To access a library use a preprocessor directive to add itsdefinitions to your program file

#include

The using statement makes syntax less clumsy Without it

std::string s = "Sharp";

std::string t = "Spiffy";

With it

using namespace std; // std contains string

string s = "Sharp";

string t = "Spiffy";


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EzWindows Library Objects

Definitions are the same form as other objects

Example

SimpleWindow W;

Most non-fundamental classes have been created so that anobject is automatically initialized to a sensible value

SimpleWindow objects have member functions to process

messages to manipulate the objects

Most important member function is Open() which causesthe object to be displayed on the screen

Example

W.Open();


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An EzWindows Program

#include

using namespace std;

#include "ezwin.h"

int ApiMain() {

SimpleWindow W("A Window", 12, 12);

W.Open();

cout a;

return ;

}


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An EzWindows Project File


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Sample Display Behavior


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RectangleShape Objects

EzWindows also provides RectangleShape for manipulatingrectangles

RectangleShape objects can specify the following attributes

SimpleWindow object that contains the rectangle (mandatory)

Offset from left edge of the SimpleWindow

Offset from top edge of the SimpleWindow

Offsets are measured in centimeters from rectangle center

Width in centimeters

Height in centimeters

Color

color is an EzWindows type


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Examples

SimpleWindow W1("My Window", 2 , 2 );

SimpleWindow W2("My Other Window", 15, 1 );

RectangleShape R(W1, , 2, Blue, , 2);

RectangleShape S(W2, 5, 2, Red, 1, 1);

RectangleShape T(W1, , 1, Black, , 5);

RectangleShape U(W1, , );


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Some RectangleShape member functions for processingmessages

Draw()

Causes rectangle to be displayed in its associatedwindow

GetWidth()

Returns width of object in centimeters

GetHeight()

Returns height of object in centimeters

SetSize()

Takes two attributes -- a width and height -- that areused to reset dimensions of the rectangle


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Another EzWindows Program

#include


#include "rect.h"

int ApiMain() {

SimpleWindow W("Rectangular Fun", 12, 12);

W.Open();

RectangleShape R(W, 5. , 2.5, Blue, 1, 2);

R.Draw();

cout Response;

return ;

}


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Sample Display Behavior


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Compound Assignment

C++ has a large set of operators for applying an operation toan object and then storing the result back into the object

Examples

int i = ;

i += ; // i is now 7

cout


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Increment and Decrement

C++ has special operators for incrementing or decrementing anobject by one

Examples

int k = ;++k; // k is 5

k++; // k is 6

cout


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Class string

Some string member functions

size() determines number of characters in the string

string Saying = "Rambling with

Gambling";

cout


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Class string

Auxiliary functions and operators

getline() extracts the next input line

string Response;

cout


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Class string

Auxiliary operators

+ string concatenation

string Part1 = "Me";

string Part2 = " and ";

string Part = "You";

string All = Part1 + Part2 + Part ;

+= compound concatenation assignment

string ThePlace = "Brooklyn";

ThePlace += ", NY";


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#include


int main() {cout


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