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Object Oriented Programming Dr. Alon Schclar

Object Oriented Programming Dr. Alon Schclar. Based on slides by Elhanan Borenstein (now at Stanford http://www.stanford.edu/~ebo/). Agenda. Administration Course Overview Introduction to OOP and C++ Function Overloading & Default Parameters Arguments By Reference cin / cout

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Object Oriented Programming Dr. Alon Schclar

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  1. Object OrientedProgrammingDr. Alon Schclar Based on slides by Elhanan Borenstein (now at Stanford http://www.stanford.edu/~ebo/)

  2. Agenda • Administration • Course Overview • Introduction to OOP and C++ • Function Overloading & Default Parameters • Arguments By Reference • cin / cout • Inline Functions • Memory Allocation • Additional Improvements

  3. Administration Course Page • Web: http://www2.mta.ac.il/~amirk/cpp/2010 • Exercises • Presentation & Example from class • E-Mail: alon.schclar@gmail.com • Reception hour: Tuesday 14-15 (prior email please) • Where: Weston 332 Books • Object Oriented Programming and C++ / Amir Kirsh • The C++ Programming Language / Bjarne Stroustrup • Effective C++, More Effective C++ / Scott Meyers

  4. Course Overview • OOP vs. C++ (can write any C++ app in c) Knowledge of C is required!!! Syllabus (partial !!!) • Introduction to OOP • C++ • Overloading functions & operators • Classes & Objects • Inheritance & Polymorphism • … • Templates & STL • Introduction to OOD

  5. Introduction to OOP and C++ Why OOP? • “Software Crisis” in procedural programming: • Too many modules… • Too many functions… An expensive mess!!! • Too many variables… • Better organization of the code • Smaller code • Reuse of code • In C – function pointers – not elegant • Easier design, analysis and implementation • Easier and more efficient scalability

  6. Introduction to OOP and C++ The Solution - Classes • The natural solution: focus on data!!! • instead of focusing on operations - functions • Define the data entities we want to use… • Each entity is implemented as a class and defines: • The data we want to store. • The operations that could be applied to this data. • Example: • College administration • Students – details, registration, tuition • Courses • Registration to courses

  7. Introduction to OOP and C++ The Solution - Classes • Classes • Objects – are instances of class • Like structs (~classes) and variable of type struct (~objects) • Still need a procedural application to create and use the objects • However – can create wrap in a managing class

  8. Introduction to OOP and C++ C++ • An Object-Oriented extension of C. • Any C program is also valid in C++ • Backward compatibility • Still contains non-OOP characteristics • global variables and functions • As before – everything starts at main • Still using pointers !!!! • Java and C# do not have pointers - references, garbage collection • Contains many cosmetic improvements • ‘//’ for one line comments

  9. Introduction to OOP and C++ C++ main OO elements • Encapsulation • data and functionality under the same roof - class • Inheritance • Define a new class based on an existing one • Polymorphism • Powerful mechanism for reusability • Template (example: swap) (C++ only) • Powerful mechanism for reusability – same code for different types • Can be done in C using the precompiler • Exceptions (C++ only)

  10. Chapter 3Before Classes…

  11. Function Overloading Motivation and Usage • Avoid writing / knowing / using a huge number of functions which in effect, do the same action. How? • Define numerous functions with the same name • Different interface (prototypes) - arguments • as long as the compiler can distinguish according to its arguments which function should be used. void printNice(int i);void printNice(int i, char ch);void printNice(int i, char* str);void printNice(float f);

  12. Function Overloading Example from booklet • void doSomething (int t) ; • void doSomething(int t, char ch); • void doSomething (int t, char* string) ; • void doSomething (float t) ; • void main ( ) • { • doSomething (13); // calls line 1 function • doSomething (2.5f) ; // calls line 4 function • doSomething (3, ‘A’) ; // calls line 2 function • doSomething (4.5f, "H") ; // calls line 3 function! • // Auto casting on 1st argument • doSomething(3, 4.5f); // calls line 2 function • / / Auto casting on 2nd argument • }

  13. Function Overloading The Ambiguity Problem • When the compiler cannot positively determine which function should be used, it will announce an ambiguity error. • Ambiguity problem – who’s fault is it? • The calling not the definition (unless two similar functions) void printNice(double d);void printNice(float f); printNice(3); // which function is invoked ?

  14. Function Overloading Example from booklet • void LetsHaveFun (float f) ; • void LetsHaveFun (double d) ; • void main ( ) • { • LetsHaveFun (3.5f) ; // Fine - goes to line 1 function • LetsHaveFun(3.12) ; // Fine - goes to line 2 function • LetsHaveFun( (float)3) ; // goes to line 1 function • LetsHaveFun( (double)3); // goes to line 2 function • LetsHaveFun(3); // Error - ambiquity • // Compiler can't decide what casting to perform ... • // int to floatorint to double • // (there aren't any rules for this) • }

  15. Function Overloading The Ambiguity Problem • Can we solve an ambiguity problem according to the return value? Why? • It is not mandatory to assign the returned value to a variable of the same type // These two function can't live together.. . int Coffee (int type) ; // returns coffee price char* Coffee(int type); // returns coffee type as string void main() { printf ("%d", Coffee (2) ) ; } Already a problem

  16. Default Parameters Usage • It is possible to define default values for the last arguments of a function. • These arguments can then be dropped when calling the functions. • It is still possible to give a different value when calling the function (all previous arguments must be specified too). • Arguments order – first (frequent non-default), last - rest • Default values are defined in the function prototype !!! (use a comment notation in the implementation…) • Compiler fills the missing values void printReallyNice(char* str, int fontSize = 10, char color = 0);

  17. Default Parameters Example from booklet • Message(char* Message, int x=1, int y=1, int color=1); • void main() • { • Message("Ma Shlornhem haiom?"); • Message ("Ifm fine", 10, 10); • Message("Ma Shlom Shlomo?", 20, 20, BLUE); • } • Message (char* Message, int x, int y, int color) • { • // Implementation of function Message • }

  18. Default Parameters Beware of ambiguity – from booklet // Default before required parameters - can't go int BuildArr(int num=10, int* arr); // Correct way: int BuildArr (int* arr, int num=10) ; // function WhichMovie - old and new version int WhichMovie(int Cinema, int HallNurn); int WhichMovie(int Cinema, int HallNum=1, int City=1); // Can't survive both // Correct way: keep the boldface line

  19. By Reference (ByRef) Arguments Argument in C • In C, arguments are passed by Value. Changing the value of the arguments in the function, does not change the value of the original variables. • If we wish to change the value of the original arguments, we can use pointers. Examples on page 27 Argument in C++ • In C++, arguments are still passed by Value, but… • A function can ask to get an argument by reference (ByRef). • Internally implemented with pointers • Hidden from the user – a safer and more elegant

  20. ByRef Arguments Example from booklet - BAD 1. void swap (int, int) ; 2. 3. void main() 4. { 5. int a, b; 6. printf("a=%d b=%dW, a, b) ; 7. swap(a,b) ; 8. printf("a=%d b=%d" , a, b) ; 9. } 10. 11. void swap(int A, int B) 12. { 13. int temp=A; 14. A=B; 15. B=temp; 16. }

  21. ByRef Arguments Example from booklet – C style – works but not C++ 1. void swap(int* A, int* B) 2. { 3. int temp=*A; 4. *A=*B; 5 . *B=temp; 6. } 7. 8. void main ( ) 9. { 10. int a, b; 11. ... 12. // send the address of a and b ! ! ! 13.swap(&a,&b); 14. ... 15. }

  22. ByRef Arguments Example from booklet – Finally C++ 1. void swap(int& A, int& B) 2. { 3. int temp=A; 4. A=B; 5 . B=temp; 6. } 7. 8. void main ( ) 9. { 10. int a, b; 11. ... 12. // send a nd b – not by address (pointers) – by Ref 13.swap(a, b); 14. ... 15. }

  23. By Reference (ByRef) Return Values • A function can return a value by reference. • In effect returns a location in memory • A by reference return value must be alive after the function terminates (global, input variables, …). • Beware of dangling refs (refs to local variables0 • Can be used as LValue in assignment • Example: Find() • Returns a ref to a searched array cell • Page 29 • What will happen if find=6 ?

  24. Ref LValues Example from booklet – • #include <iostream.h> • #include <stdio.h> • #include <conio.h> • void PrintArr(int* arr, int size) • { • for(int i=0; i<size; i++) • { • printf("%d, ", arr[i]); • } • printf("\n"); • }

  25. int& GetOut(int* arr, int size, int& LookFor) { for(int i=0; i<size; i++) { if(arr[i]==LookFor) return arr[i]; } return LookFor; }

  26. void main() { int Arr[]={1,4,2,5,3}; int size=sizeof(Arr)/sizeof(Arr[0]); PrintArr(Arr, size); int find=5; GetOut(Arr, size, find)=13; PrintArr(Arr, size); getch(); }

  27. By Reference (ByRef) variables • Like a synonym • Mainly used for inheritance polymorphism 1. int i=3; 2. int j=5; 3. // Reference variable must be initialized in declaration 4. // int &k; - Error – no initialization 5. int &k=i; 6. k=31; // means - i=31 7. k=j; // means - i = j 8. j=12; // doesn't change i or k 9. i=8; // k becomes 8 10. printf("i=%d, k=%d”, i, k); // prints : i=8, k=8

  28. Input & Output (cin, cout) I/O in C • When using printf (or scanf), the programmer must define the type of each argument. • We could write a different function for each type • Not elegant – many similar names I/O in C++ • We can use the I/O objects cin and cout • (defined in <iostream.h>) can be further overloaded • We will use the operators “<<“ and “>>” (like +) • Thanks to function overloading, there is no need to define the type of the arguments.

  29. Input & Output (cin, cout) Example 1 (output) #include <iostream.h>void main( ){ int i = 23; char *str = “hello”; cout<<str; cout<<i<<endl; cout<<“the value of i is “<<i<<endl; cout<<(char)65;}

  30. I/O Example from booklet – • 1. #include<iostream.h> • 3. void main() • 4. { • 5. int i=5; • char* string="This is great \n”; • cout <<string; • cout<<i<<endl; // endl - means end-of-line = “\n” • 9. // The compiler doesn't get confused, I • 10. // even i f we pull one over on it: • 11. cout<<"This is int:"<<4.5; • 12. // And we can tell a whole story in one line ! • 13. cout<<"i="<<i<<"r string="<<string<<endl; • 14. cout<<'A’; // prints the character A • 15. cout<<65; // prints the number 65 • 16. cout<<(char)65; // prints the character A • 17. }

  31. Input & Output (cin, cout) Example 2 (input) #include <iostream.h>void main( ){ int age; char str[100]; cout<<“Please enter your name”; cin>>str; cout<<“Please enter your age”; cin>>age;} No pointers – how ?

  32. I/O Example from booklet – 1. #include<iostream. h> 3. void main ( ) 4. { 5. int i; 6. char string [40] ; 7. char ch; 8. 9. cout<<"Please be kind enough to type a string:"; 10. cin >> string ; 11. // The next word - till a white space - will enter into 12. // the char array named string . 13. // Same as: scanf("%s”, string ) ; 14. 15. cout<<"Now please be friendly and give me int: "; 16. cin>>i; 17. // The next word - will be converted to int and entered 18. // into i. Same as: scanf("%d”, &i); 19. 20. cout<<"Now please be helpful and provide one char: "; 21. cin>>ch; 22. // The first char entered will go into ch. 23. // Same as: scanf("%c”,& ch); 24. }

  33. Inline Functions Motivation • Each function call requires allocating memory on the stack. • Overhead may outweighs the benefits (especially in small functions that will be called many times). • Macros have other problems: • No type checking on the arguments • Readability • Side effect i++

  34. Inline Functions The solution • Inline functions. • The functions are embedded within the call - replicated • The compiler is not bound by the inline declaration. • In case too long, missing return etc. -> no inline for you • In debug – must specify – otherwise it is a warning • Must implement in the file where used • or include in .h file • Bigger exe – the same as macros

  35. Inline Functions Examples from booklet – 1. #define ROUND (num) (int) ( (num) + 0.5) 2. 3. inline int round(double num) 4. { 5. return (int) (num+0.5); 6. } 1. #define SQUARE (num) (num) * (num) 2. 3. inline double square(double num) 4. { 5. return (num*num); 6. }

  36. Memory Allocation Allocation • Memory allocation is implemented with the command “new”. • No casting, sizeof is required (unlike C). • For arrays allocation we will use “new[n]”. Freeing • To free allocated memory, we will use the command “delete”. • For arrays, we will use “delete[ ]”.

  37. Memory allocation Example from booklet – 1. char* string; 2. string=new char[20]; 3. cout<<"Please insert string: "; 4. cin>>string; 5. 6. int* pInt=new int; 7. cout<<"Please insert int: "; 8. cin>>*pInt; 9. 10. int n; 11. cout<<"What is the size of the array? "; 12. cin>>n; 13. float* FloatArr=new float[n]; 14. ... 15. 16. delete [ ]string; 17. delete pInt; 18. delete [ ]FloatArr;

  38. 13. // depends on the options marked in the compiler ! ! !) 14. for (int i=0; i<temp; i++) 15. { 16. // item is declared again and again 17. // for every entry in the loop 18. int item=GetItem (i) *13; 19. ImportantVar+=item; 20. } 21. // The following line may be allowed, depending 22. // on the options marked in the compiler ... 23. cout<<i; 24. ... 25. }

  39. Additional Improvements Comments • C++ still supports the conventional notation of comments from C: /* this is a comment */ • In addition, we can use a single comment line starting with // // initialization int index; // this is also a comment

  40. Additional Improvements Variable Definition • Variables can be defined at any point in the code. • Should be used wisely!!!! 1. void main() 2 . { 3 . int ImportantVar; // controls for the nuclear explosion 4. ... 5. cout<<"Haide Sara"; 6. ... 7. // We define here the variable temp to hold the outcome 8. // of the function 'GoGetItf 9. int temp=GoGetIt ("Hu-Ha") ; 10. 11. // The loop index i is declared here inside the for ! 12. // (The question whether i is available after the loo;,

  41. Additional Improvements Structs and enums Definition • When defining a struct or enum variable, no need to declare it is a struct / enum. • Reminder: in C we usually used typedef for this problem 1. struct Student 2. { 3. char* StudentName; 4. int MoneyResources; 5. // etc. 6. }; 7. 8. void main ( ) 9. { 10. Student Dudu; / / in C: struct Student Dudu 11. }

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