CS1061: C Programming Lecture 22: A Brief Look at C++

1. CS1061: C ProgrammingLecture 22: A Brief Look at C++ A. O’Riordan, 2004

2. Object Oriented Programming • C++ is an object-oriented programming language (OOPL) based on C. • Programmers define entities called objects and define communication between the objects in the form of (member) function invocation. • Objects may consist of both program logic and data. • Programming consists of defining classes of these objects and their interrelationships, i.e. behaviour.

3. C++ = C + Objects • C++ is based on C. C++ gets its name from the C increment operator ++. • C++ was an attempt to invent a programming language that supported "object oriented" abstractions, yet remained compatible with the widely used C language. • Thus programmers can reap the benefits of object orientation without having to throw away their existing C programs. • C++ is nearly-but not exactly-a superset of ISO C.

4. The C++ Language • C++ was developed by Bjarne Stoustrup at AT&T in the 1980s, but only became an ISO standard in 1998. • C++ is a problematic language. For example the pointer implementation is considered too low-level. Also there is no automatic garbage collection, i.e. you cannot automatically reclaim used memory when it becomes available. It has complex semantics, and is hard to learn. • Modern languages such as Java and C# aim to combat and remedy many of these disadvantages. • http://java.sun.com/ • http://msdn.microsoft.com/vcsharp/

5. C versus C++ Many constructs in C and C++ are the same (or almost exactly the same) • Assignment Statement • Arithmetic • Looping – for, while, do..while • Decision Statements – if, switch • Arrays and Pointers • Logic and Relational Operaters Other aspects of the language are quite different • Data Definition – struct versus class • Function Invocation – messages in C++ • Input/Output

6. Input/Output Input/output is also significantly different in C++ and is based on streams. Here is the "HelloWorld" program. #include<iostream> using namespace std; int main(){ // Display HelloWorld on the screen cout << "HelloWorld" << endl; return(0); }

7. Example with Function Call #include <iostream> using namespace std; void display_char(char); int main(){ char my_c; cin >> my_c; display_char(my_c); return 0; } void display_char(char c){ cout << "Character is " << c << endl; return; }

8. String example Here is a simple example – need to include sting header file. #include <string> using namespace std; int main(){ string salutation = "Hello\n"; cout << salutation; return 0; }

9. Reference Parameters An alternative is pointers is available in C++. This is to use reference parameters: #include<iostream> void add_VAT(float); int nain(){ add_VAT(priceItem); cout << "Price plus VAT is " << priceItem << endl; return 0; } void add_VAT(float &refPriceItem){ refPriceItem*= (1 + VATRate); }

10. Class Concept • Objects consist of both data and functionality. • In C++ this equates to data members and member functions. • Classes in C++ are implemented as an extension of the struct mechanism in C. • A fundamental construct in object oriented programming is that of inheritance. It is common when classifying things in the real world to order them into hierarchical structures. We can likewise arrange C++ classes into hierarchies.

11. Permissible operations Data Private Public Encapsulation In C++ we encapsulate the data and functions in a class. The elements of the class are called members. Here is an example of a bank account class. class DepositAccount{ public: DepositAccount(int accnum); void makeWithdrawal(int amt); void makeLodgement(int amt); void printStatement(); private: int accountNumber; float balance; };

12. Member Functions • An example member function implementation is given here: void DepositAccount::makeWithdrawal(int amt){ if (amt > balance) cout << "You do not have enough in account" << endl; else balance -= amt; } • And called as follows: DepositAccount my_da; my_da.makeWithdrawal(100);

13. More on C++ For treatment of the C++ language there are numerous excellent books. Here are two: • The C++ primer, 3rd edition, Stanley B. Lippman, Addison-Wesley, 1998. • The C++ Programming Language, 3rd edition, Bjarne Stroustrup, Addison-Wesley, 1997.