07 oo exercise

8/13/2019 07 Oo Exercise

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Classes

7. OO Revisited

June 15, 2010

7. OO Revisited

Introduction to C/C++,Tobias Weinzierl page 1 of 14
http://www5.in.tum.de/wiki/index.php/Dr._rer._nat._Tobias_Weinzierlhttp://www5.in.tum.de/wiki/index.php/Dr._rer._nat._Tobias_Weinzierl


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Classes

Create a Struct Vector

Create a structVectorwith three doubles and an additional double holding the

length of the vector.

7. OO Revisited



3/23

Classes




s t r u c t Ve cto r {double x [ 3 ] ;double l e n g t h ;

} ;

Create three vectorsa= (0.2, 0.4), b= (1.0, 0.0), andc= (1.2, 0.0)in yourmain routine. The first two instances shall be variables, the latter instance shall becreated on the heap.

7. OO Revisited



4/23

Classes





} ;

Create three vectorsa= (0.2, 0.4), b= (1.0, 0.0), andc= (1.2, 0.0)in yourmain routine. The first two instances shall be variables, the latter instance shall becreated on the heap.

V e ct o r a , b ;Ve cto r c = new V e c t o r ;/ / a s s i g n v a l u es now

7. OO Revisited



5/23

Classes

Compute the Length

Write an operation void computeLength( Vector & vector)that computes the

length of the passed vector and sets it accordingly.

7. OO Revisited



6/23

Classes

Compute the Length



# i n c l u d e


} ;

v o i d co mp ut eL en gt h ( V e c t o r& v e c t o r ) {v e c to r . l e n g t h = s t d : : s q r t ( v e ct o r . x [ 0 ]v e ct o r . x [ 0 ] + v e ct o r . x [

}

Call this operation in your main for aand c.

7. OO Revisited



7/23

Classes

Compute the Length



# i n c l u d e


} ;

v o i d co mp ut eL en gt h ( V e c t o r& v e c t o r ) {v e c to r . l e n g t h = s t d : : s q r t ( v e ct o r . x [ 0 ]v e ct o r . x [ 0 ] + v e ct o r . x [

}

Call this operation in your main for aand c.

compu teL en gth (a ) ;computeLength(c ) ;

7. OO Revisited



8/23

Classes

Methods Instead of Functions

Makevoid computeLength( Vector & vector)a method ofVector.

7. OO Revisited



9/23

Classes



# i n c l u d e

s t r u c t Ve cto r {double x [ 3 ] ;double l e n g t h ;v o i d computeLength ( ) ;

} ;

v o i d Vect or : : computeLength ( ) {l e ng t h = s td : : s q r t ( x [ 0 ] x [ 0 ] + x [ 1 ] . . . ) ;

}

a . computeLength ( ) ;c>computeLength ( ) ;

Add an operation toTerminal()writing the vector to the terminal.

7. OO Revisited



10/23

Classes



# i n c l u d e

s t r u c t Ve cto r {double x [ 3 ] ;double l e n g t h ;v o i d computeLength ( ) ;

} ;

v o i d Vect or : : computeLength ( ) {l e ng t h = s td : : s q r t ( x [ 0 ] x [ 0 ] + x [ 1 ] . . . ) ;

}

a . computeLength ( ) ;c>computeLength ( ) ;

Add an operation toTerminal()writing the vector to the terminal.

v o i d V e c t o r : : t o T e r m i n a l ( ) {s t d : : c ou t


11/23

Classes

Scalar Product

Add the operation double getAngle( const Vector & rhs)to Vector. Thisoperation shall do two things:

Print object for which it is called to terminal. Print argumentrhs to terminal. Return 0.0.

Invoke this operation for the variablesaand cand print the result to the terminal.

7. OO Revisited



12/23

Classes

Scalar Product

Add the operation double getAngle( const Vector & rhs)to Vector. Thisoperation shall do two things:

Print object for which it is called to terminal. Print argumentrhs to terminal. Return 0.0.

Invoke this operation for the variablesaand cand print the result to the terminal.

# i n c l u d e

s t r u c t Ve cto r {double x [ 3 ] ;double l e n g t h ;double getAngle ( co n st V ec t or & r h s ) ;

} ;

double Ve cto r : : g e tAn g le ( co n st V e ct o r & r h s ) {

t o T er m i n al ( ) ;r h s . t o T e r mi n a l ( ) ;r e t u r n 0 . 0 ;

}

. . .a . ge t A n gl e (c ) ;/ / o r

c>g e t A ng l e ( a ) ;7. OO RevisitedIntroduction to C/C++,Tobias Weinzierl page 5 of 14


13/23

Classes

Scalar Product

Add the operation double getAngle( const Vector & rhs)to Vector. This

operation shall do three things: Print object for which it is called to terminal. Print argumentrhs to terminal. Compute angle between object andrhs due to the value oflengthand

return it.

Invoke the operation foraand b.

7. OO Revisited



14/23

Classes


15/23

Classes

Scalar Product

Add a constructor to Vectorwhich accepts three doubles and automatically

ensures thatlengthholds the right value. Do not use initialisation lists (makes it alittle bit simpler).

7. OO Revisited


Classes


16/23

Classes

Scalar Product

Add a constructor to Vectorwhich accepts three doubles and automatically

ensures thatlengthholds the right value. Do not use initialisation lists (makes it alittle bit simpler).

# i n c l u d e

s t r u c t Ve cto r {. . .Vect or ( double x1 , double x2 , double x3 ) ;

} ;

Ve cto r : : Ve cto r ( double x1 , double x2 , double x3 ) {x [ 0 ] = x1 ; . . .computeLength ( ) ;

}

Make your struct a class and try to manipulate the attribute length of amanuallywithin the main function.

7. OO Revisited


Classes


17/23

Classes

7.1.Classes

With the new technique at hand, we can encapsulate data and operations asthese two things go hand in hand.

We can write a couple of setter and getter operations to allow the user tomanipulate our brand new data structure.

However, the user still can reset attributes manually. We can not forbid this.

Consequently, we need an alterantive, a new technique to forbid this.

Furthermore, it would be nice if the user doesnt even see the attributes, as

it might be reasonable that the user cant even read attributes if we dont providethe corresponding getters (next pointer in our list example, e.g.).

7. OO Revisited


Classes


18/23

Classes

Our Beloved Colleagues

/ R e p r es e n ts a d a t e .

Each m onth s h a l l ha ve 30 d ay s ./

s t r u c t Date {i n t month , day ;v o i d switchToNextDay ;

} ;

/ / t h i s i s t h e co de our c o l l e a g u e wroteDa te myDate ( . . . ) ;myDate. day++;

7. OO Revisited


Classes


19/23

Encapsulation



c l a s s Da te {p r i v a t e :

i n t month , day ;p u b l i c :

v o i d switchToNextDay ( ) ;} ;

In principle, classis an alias forstruct,

i.e. we can do all the things we can do with structs with classes, too.

However, for classes we can create publicand privatesections. Only add themin the header.

Private attributes and operations are not available from outside, but only within theoperations of the class (encapsulation).

7. OO Revisited


Classes


20/23

Encapsulation at Work




i n t m on th , d a y ;p u b l i c :

v o i d switchToNextDay ( ) ;} ;

. . .v o i d Date : : switchToNextDay ( ) {

d a y++; / / o . k .}

Date myDate;

myDate. day ++; / / doe sn t w or k .

7. OO Revisited


Classes


21/23

Encapsulation and the Object Lifecycle




i n t m on th , d a y ;D at e ( ) ;

p u b l i c :v o i d switchToNextDay ( ) ;

Da te ( i n t month , i n t day ) ;} ;

We can make constructors private and, thus, forbid everybody to create aninstance of our object.

We could make the destructor private, too. However, this never makes sense.

7. OO Revisited


Classes


22/23

Remark: Classes and Namespaces

namespace cal end ar {

/ R e p r es e n ts a d a t e . Each m onth s h a l l ha ve 30 d ay s ./

c l a s s D at e {p r i v a t e :

i n t m on th , d a y ;D at e ( ) ;

p u b l i c :

v o i d switchToNextDay ( ) ;Da te ( i n t month , i n t day ) ;

} ;}

v o i d cal enda r : : Date : : switchToNextDay ( ) {. . .

}

/ / f u l l y q u a l i f i e d ar gum ent here n o t necessary/ / we ca n access p r i v a t e arguments o f o t h e r i n s t a n c e sv o i d cal enda r : : Date : : copyFromOtherDate (co n st ca le n d a r : : Date& d a te ) {

. . .}

7. OO Revisited


Classes


23/23

Remark: Classes and Recursion

c l as s I n t e g e rE n t r y {

p r i v a t e :i n t value ;I n t e g e r E n t r y next ;

p u b l i c :v o i d append ( I n t e g e r E n t r y newEntry ) ;

} ;

v o i d I n t e g e r E n t r y : : append ( I n t e g e r E n t r y newEntry) {

i f ( next ==0) {n e xt = n e wEn try ;

}e l s e {

next>append(newEntry );}

}

This is not recursion, as the operation is invoked on another object.

However, recursion and object-based programming work together.

7. OO Revisited


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