1. Introduction to C++
Professor Hugh C. Lauer CS-2303, System Programming Concepts
(Slides include materials from The C Programming Language, 2nd edition, by Kernighan and Ritchie, Absolute C++, by Walter Savitch, The C++ Programming Language, Special Edition, by Bjarne Stroustrup, and from C: How to Program, 5th and 6th editions, by Deitel and Deitel)
CS-2303, A-Term 2012
Introduction to C++

2. Reading Absolute C++, Chapter 1 Absolute C++, Chapter 6 Advice
Tour of C++
Absolute C++, Chapter 6
Classes and structs
Advice
Don’t panic! All will become clear in time.
You don’t need to know every detail of C++ to write good programs
Focus on programming techniques, not language details
CS-2303, A-Term 2012
Introduction to C++

3. What Is C++? A federation of (at least) four languages
Note: Objective C was invented at about the same time, with similar goals.
What Is C++?
A federation of (at least) four languages
C — with a few minor syntactic differences
Files & I/O
Use new and delete instead of malloc() and free()
Inline Functions …
Template C++
For defining and creating templates
Object-oriented C++
Classes
Inheritance and Multiple Inheritance
Function and Operator Overloading
References and Reference Parameters
Default Arguments
Standard Template Library
Many tools
Templates for containers
CS-2303, A-Term 2012
Introduction to C++

4. Compiling C++ Use gcc, Eclipse, Visual Studio, etc. File types
See Lab #1
File types
.cc, .cp, .cpp, .CPP, .cxx, .c++, .C
.h, .H
In Linux
gcc will recognize C++ file extensions and compile them
but won’t get the libraries and defaults right
g++ will set language to C++ and link to correct libraries by default
Some of these have special properties.
CS-2303, A-Term 2012
Introduction to C++

5. In this Topic A Simple C++ Example
C++ Input/Output
Similarities and differences between C and C++
Brief tour of Chapters 4 & 5
References and Reference Parameters
Namespaces
Including scope resolution operator "::"
CS-2303, A-Term 2012
Introduction to C++

6. A Simple C++ Example // C++ simple example C++ style comments
#include <iostream> //for C++ Input and Output
int main () {
int number3;
std::cout << "Enter a number:";
std::cin >> number3;
int number2, sum;
std::cout << "Enter another number:";
std::cin >> number2;
sum = number2 + number3;
std::cout << "Sum is: " << sum <<std::endl;
return 0; }
C++ style comments
standard output stream object stream insertion operator
stream extraction operator
standard input stream object
stream manipulator
Concatenating insertion operators
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Introduction to C++

7. Simple C++ Program (continued)
<iostream>
Must be included for any program that outputs data to the screen or inputs data from the keyboard using C++ style stream input/output.
Replaces <stdio.h> of C
C++ requires you to specify the return type, possibly void, for all functions.
Specifying a parameter list with empty parentheses is equivalent to specifying a void parameter list in C.
CS-2303, A-Term 2012
Introduction to C++

8. Notes on Simple C++ Program
Stream manipulator std::endl
Outputs a newline.
Flushes the output buffer
The notation std::cout specifies a name (cout) that belongs to the namespace std.
Note: std::ends flushes the buffer but does not add newline.
To be explained later
CS-2303, A-Term 2012
Introduction to C++

9. Header Files C++ Standard Library header files
Each contains a portion of the Standard Library.
Function prototypes for the related functions
Definitions of various class types and functions
Constants needed by those functions
“Instruct” the compiler on how to interface with library and user-written components.
Use #include directive to include class or interface in a program.
Note: You may encounter standard header file names ending in .h or .H
These are “old-style” header files
They are superseded by the C++ Standard Library header files
CS-2303, A-Term 2012
Introduction to C++

10. C++ Standard Library header files
<iostream>
<iomanip>
<fstream>
<ifstream>, <ofstream>
<string>
<cstring>
<cstdlib>
<cmath>
<complex>, <numeric>
<ctime>
<iterator> …
<vector> <list> <queue> <stack> <deque> <map> <set> <bitset>
CS-2303, A-Term 2012
Introduction to C++

11. Libraries for Next Assignment
For PA4
<ifstream>
stream input from file
<ofstream>
stream output to file
<string>
String management
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Introduction to C++

12. Keywords Shared with C
CS-2303, A-Term 2012
Introduction to C++

13. New Keywords in C++
CS-2303, A-Term 2012
Introduction to C++

14. Types and Declarations
Integer and floating point types
Much like C
bool
Values true and false
Use instead of C zero and non-zero
char and wchar_t
char: usually 8 bits, implementation dependent
wchar_t: larger character sets – Unicode, international character sets, etc.
Enumerations
Like C
Declarations, initializations, typedefs
A lot like C
Beware! C++ will convert between integers and bool without telling you!
CS-2303, A-Term 2012
Introduction to C++

15. Ch. 5 – Pointers, Arrays, and Structs
Pointers — like pointers in C
May point to any type T or to void
Unary '&' operator means “create a pointer”
Unary ‘*' operator means “dereference a pointer”
Simple arrays
A lot like C
May have any type T as elements
Related to pointers as in C
However,
Use vector or valarray containers from Standard Template Library (STL)
Recommend Advice:– Use 0 (i.e.,zero) instead of NULL
CS-2303, A-Term 2012
Introduction to C++

16. Ch. 5 – Pointers, Arrays, and Structs (continued)
In C, we introduced a struct as “like a Java class, but with no methods”
In C++, a struct IS A class!
The keyword struct can be used wherever the keyword class can be used
An vice versa!
The ONLY difference is that members of a struct are, by default, public
class members are by default private
public and private access specifiers may be included anywhere in a struct or a class
CS-2303, A-Term 2012
Introduction to C++

17. structs and classes (continued)
By definition:–
struct s { …
is shorthand for
class s { public: …
Stylistic advice:–
Use struct when ALL members are public; otherwise, use class
CS-2303, A-Term 2012
Introduction to C++

18. struct example Example:– Usage:–
struct address{ char * name; long int number; char * street; char * town; char state[2]; long zip;
}; //requires a semicolon after '}'
Usage:–
address jd; // don’t need to say “struct” as we did in C
jd.name = “Jim Dandy”;
jd.number = 61;
CS-2303, A-Term 2012
Introduction to C++

19. Type Equivalence
Two structs are different types, even when the have identical members
§5.7.1
Example
struct S1 { int a; };
struct S2 { int a; };
S2 = S1; // illegal!
CS-2303, A-Term 2012
Introduction to C++

20. Questions?
CS-2303, A-Term 2012
Introduction to C++

21. Memory Allocation from Heap
new and delete for structs, classes, etc.
Example
class Table { …} … Table *p = new Table; //allocate and initialize Table *q = new Table; //new objects from Heap … delete p; // free objects, clean up, delete q; // return memory to Heap
See §10.1, Absolute C++
CS-2303, A-Term 2012
Introduction to C++

22. Memory Allocation (continued)
new and delete[] for arrays
Example
char * s = new char[length]; // allocate new arrays int * t = new int[count]; // from Heap … s[i] = 'x'; // use arrays as in C int x = t[j]; … delete[] s; // free whole arrays, return delete[] t; // memory to Heap
See §10.2
It is usually incorrect to say
delete s; delete t;
CS-2303, A-Term 2012
Introduction to C++

23. Memory Allocation (concluded)
Always use new and delete or delete[]
Never, ever use malloc() and free()
malloc() doesn’t correctly initialize objects
Especially class objects!
free() doesn’t correctly destroy objects
delete doesn’t correctly destroy individual objects of arrays
Must use delete[]
CS-2303, A-Term 2012
Introduction to C++

24. Questions?
CS-2303, A-Term 2012
Introduction to C++

25. BIG difference from Java
References in C++
Definition Reference:– An Alternative Name for an object
BIG difference from Java
References are only created in declarations and parameters
A reference can only appear where the object itself could have appeared
See §8.3 in Absolute C++
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Introduction to C++

26. Simple References
void f() { int j = 1; int &r = j; //r and j refer to the exact same int int x = r; // x now is 1 r = 2; // j now is 2 } //f int k; int &r1 = k; // okay: r1 is initialized int &r2; // error; initializer missing extern int &r3; //okay; r3 defined elsewhere
Sometimes, reference declarations are written as
int& r1 = k;
CS-2303, A-Term 2012
Introduction to C++

27. Simple References (continued)
This '&' is the unary address operator brought over from C
It is used here to create a reference!
void g() { int ii = 0; int &rr = ii; rr++; // ii now is 1 int *pp = &rr; // pp now points to ii
} //g
Note: This declares a pointer exactly as in C, and initializes it with the address of rr (which is another name for ii)
CS-2303, A-Term 2012
Introduction to C++

28. Example Usage of a Reference
int grid[1000]; int rowSize, x, y;
...
int &element = grid[x*rowSize+y]; ... /* computations on integer named element */
CS-2303, A-Term 2012
Introduction to C++

29. Reference Parameters
An alias for its corresponding argument in a function call.
& placed after the parameter type in the function prototype and function header
Example
int &count in a function header
Pronounced as “count is a reference to an int”
Parameter name in the called function body actually refers to the original variable in the calling function.
CS-2303, A-Term 2012
Introduction to C++

30. Reference Parameter Example
C version
void swap (int *a, int *b) { int temp = *a; *a = *b; *b = temp;
} // void swap(…)
C++ version
void swap (int &a, int &b) { int temp = a; a = b; b = temp;
Hazard: a NULL pointer
Non-hazard: no pointer here
CS-2303, A-Term 2012
Introduction to C++

31. Notes on References and Pointers
Pointers in C do multiple duty
Links, as in linked lists and trees
Parameters, where the function needs to return a value to an argument provided by the caller
Short-hand, a short way of referring to an object that otherwise would need a complex expression …
C++ introduces references to address both of these cases
CS-2303, A-Term 2012
Introduction to C++

32. Java vs. C++ References In Java, a reference is a data type.
It can be assigned to, compared, copied, stored, etc.
Same reference variable can refer to different objects at different times during execution
In C++, a reference is an alias for an object
It cannot be assigned to; assignment is through the reference to the underlying object
Similar to dereferencing a pointer in C
It cannot be compared; comparison applies to underlying object
A reference always refers to the same object for the duration of its scope
CS-2303, A-Term 2012
Introduction to C++

33. Repeat Three Times
A C++ reference is not a pointer, … And neither of them resembles a Java reference
CS-2303, A-Term 2012
Introduction to C++

34. Questions?
CS-2303, A-Term 2012
Introduction to C++

35. Namespace A logical grouping of names
… to set them apart from other names
… to avoid conflicts among similar names
See §8.2
CS-2303, A-Term 2012
Introduction to C++

36. Namespace Example From slide #7 // C++ simple example
#include <iostream> //for C++ Input and Output
int main () {
int number3;
std::cout << "Enter a number:";
std::cin >> number3;
int number2, sum;
std::cout << "Enter another number:";
std::cin >> number2;
sum = number2 + number3;
std::cout << "Sum is: " << sum <<std::endl;
return 0; }
From slide #7
CS-2303, A-Term 2012
Introduction to C++

37. Namespaces (continued)
Names cout, cin, endl are declared in <iostream> …
… but are not directly visible to program
The are part of namespace std
… which is visible!
Need scope resolution operator '::‘
To get at things from a namespace
CS-2303, A-Term 2012
Introduction to C++

38. Scope Resolution Operator
std::cout
The object cout that is declared in namespace std
void BinaryTree::PrintTree
The method PrintTree that is declared in class BinaryTree
(needed when implementing PrintTree)
CS-2303, A-Term 2012
Introduction to C++

39. “Using” Directive
#include <iostream> using std::cout; using std::cin; using std::endl; … int main() { double sideValue; cout << "\nEnter the side " " length of your cube: "; cin >> sideValue; cout << "Volume of cube with “ "side " << sideValue << " is " << cube( sideValue ) << endl; return 0; } // int main()
Adds cout, cin, endl from namespace std to current scope
These names may now be used without qualification
CS-2303, A-Term 2012
Introduction to C++

40. Common C++ Programming Error
Forgetting to say “Using”
You get undeclared identifiers
Even though you include the appropriate header file!
Using std
Bad style
Makes all names in namespace std visible
… whether you need them or not!
CS-2303, A-Term 2012
Introduction to C++

41. Questions?
CS-2303, A-Term 2012
Introduction to C++