Chapter 1 C++ Basics

Transcription

1 Chapter 1 C++ Basics 1 Learning Objectives Introduction to C++ Variables, Expressions, and Assignment Statements Console Input/Output Program Style Libraries and Namespaces 2

2 Introduction to C++ Origins of the C++ language Object-oriented programming The character of C++ C++ Terminology A sample C++ Program 3 Introduction to C++ Origins of the C++ language 1970, Dennis M. Ritchie, AT&T Bell Labs Dennis Ritchie Bell Labs, Rm 2C Mountain Ave. Murray Hill, New Jersey , USA dmr@bell-labs.com (office), (fax) AT&T Bell Telephony Labs. Bell Labs Lucent Used for writing and maintaining Unix O.S. A general purpose Language Major Drawbacks of C language: Not easy to understand and coding Poor code reusability Lack of exception handling mechanism 4

3 Introduction to C++ Origins of the C++ language(con t) History of C++ C++ was written by Bjarne Sroustrup at Bell Labs during C++ is an extension of C. C++ combines object-oriented features with the power and efficiency of C. The term C++ was first used in C++ was released in Introduction to C++ Object-oriented programming OOP (Object Oriented Programming) Objects and Classes Encapsulation Inheritance Polymorphism 6

4 Objects Introduction to C++ Object-oriented programming(con t) Hidden data that is accessed and manipulated through a well-defined interface Behaviours (s) things an object can do like procedures and functions in other languages Attributes (fields) information an object knows (has-a) like data and variables in other languages (records) 7 Class Introduction to C++ Object-oriented programming(con t) A template for creating objects. Defines the attributes and behaviors for one kind of object. No data is allocated until an object is created from the class. The creation (construction) of an object is called instantiation. The created object is often called an instance (or an instance of class X) 8

5 Introduction to C++ Object-oriented programming(con t) Interface Internal/private/helper s only available within the class. Attributes (Fields of the class) Defined by the class. Filled by the object. 9 Introduction to C++ Object-oriented programming(con t) Encapsulation Abstraction Information Hiding Security Attributes (Fields of the class) 10

6 Introduction to C++ Object-oriented programming(con t) Inheritance A new class created by modification of an existing class The inheriting class contains all the attributes and behaviors of the class it inherited from plus any attributes and behaviors it defines The inheriting class can override the definition of existing s by providing its own implementation The code of the inheriting class consists only of the changes and additions to the base class 11 Introduction to C++ Object-oriented programming(con t) Interface override Fields of The Object Additional Fields 12

7 Introduction to C++ Object-oriented programming(con t) Advantages of inheritance Modular coding less code, easier to understand Code reuse don t break what is already working easier updates May not have access to modify the original source code Polymorphism 13 Introduction to C++ Object-oriented programming(con t) Inheritance Terminology Class one above Parent class, Super class Class one below Child class Class one or more above Ancestor class, Base class Class one or more below Descendent class vehicle Truck Van Sedan SUV 14

8 Introduction to C++ Object-oriented programming(con t) Polymorphism to hide many implementations behind the same interface DrawRect(p1,p2) DrawHexagon(p1,p2,p3,p4,p5,p6) DrawChart DrawEllipse(p1, p2, r1, r2) DrawTriangle(p1,p2,p3) DrawCircle(p, r) DrawPentagon(p1,p2,p3,p4,p5) 15 Introduction to C++ The character of C++ Class A class is a user-defined data type Object A object is a variable of a class type Message Interacting between objects Functions/Operators overloading int print( char *s ); // Print a string. int print( double dvalue ); // Print a double. int print( double dvalue, int prec ); // Print a double with a given precision. 16

9 Template Introduction to C++ The character of C++(con t) implementation of algorithm abstraction // min for ints int min( int a, int b ) return ( a < b )? a : b; // min for longs long min( long a, long b ) return ( a < b )? a : b; template <class T> T min( T a, T b ) return ( a < b )? a : b; // min for chars char min( char a, char b ) return ( a < b )? a : b; Templates can significantly reduce source code size and increase code flexibility without reducing type safety. 17 Namespace Introduction to C++ The character of C++(con t) to accommodate more reuse of class and function names // one.h char func(char); class String {... }; // two.h class String {... }; {... String();// Which one?... } // one.h namespace one { char func(char); class String {... }; } // two.h namespace two { class String {... }; } one::string() and two::string() 18

10 Introduction to C++ The character of C++(con t) Exception handling try { buf = new char[512]; if( buf == 0 ) throw "Memory allocation failure!"; } catch( char * str ) { cout << "Exception raised: " << str << '\n'; } Memory management // Allocate on the heap char* mychararray = new char[buff_size]; int* myintarray = new int[buff_size];... delete [] mychararray; delete [] myintarray; 19 Introduction to C++ C++ Terminology Functions Procedures Methods Functions Subprograms C++ Program main() function Others the same as most other programming languages 20

11 Introduction to C++ A Sample C++ Program Program #include <iostream> using namespace std; int main( ) { int numberoflanguages; cout << "Hello reader.\n" << "Welcome to C++.\n"; console Input/Output namespace std main() int void main() numberoflanguages console cout << "How many programming languages have you used? "; cin >> numberoflanguages; if (numberoflanguages < 1) cout << "Read the preface. You may prefer\n" << "a more elementary book by the same author.\n"; else cout << "Enjoy the book.\n"; If else return 0; } 0 21 Results Introduction to C++ A Sample C++ Program(con t) 22

12 Introduction to C++ A Sample C++ Program(con t) 23 Session Summary Origins of the C++ language Object-oriented programming The character of C++ C++ Terminology A sample C++ Program 24

13 Variables, Expressions, and Assignment Statements Identifiers Variables Assignment Statements More Assignment Statements Assignment Compatibility Literals Escape Sequences Naming Constants 25 Variables, Expressions, and Arithmetic Operators and Expressions Integer and Floating-Point Division Type Casting Increment and Decrement Operators 26

14 Variables, Expressions, and Identifier The name of a variable (or other item you may define in a program) Starts with a letter or a underscore The rest of the characters must be letters, digits, or underscore symbol. Letter Underscore 27 Letter Underscore Digit Variables, Expressions, and Valid Identifiers x x1 x_1 _abc ABC123z7 sum RATE count data2 bigbonus Invalid Identifiers 12 3X %change data-1 myfirst.c PROG.CPP Case Sensitive rate RATE Rate 28

15 Variables, Expressions, and Comments for Identifiers System Identifiers Standard Libraries W1 W2 W3 lowercase lowercase lowercase uppercase uppercase topspeed, bankrate1, bankrate2, timeofarrival The length of an Identifier depends on compiler 29 Variables, Expressions, and Keywords (Appendix I) and Reserved Words 30

16 Variables, Expressions, and Variables Must be declared before it can be used It s better to declared variables at just before they are used or start of a block { Declaration examples int numberofbeans; double oneweight, totalweight; Name Any legal Identifiers 31 Variables, Expressions, and Simple Data Types (Display 1.2) Type Storage Speed Precision unsigned char, short, int, long String Pointer, Array, Classes will be discussed later. 32?

17 Variables, Expressions, and 33 Variables, Expressions, and Use meaningful names x = y * z; distance = speed * time; 34

18 Variables, Expressions, and Assignment Statements to change the value of a variable Lvalue Rvalue 35 Variables, Expressions, and Assignment statements can be used as an expression n=(m=2); The sub-expression (m=2) changes the value of m to 2 and returns the value 2. n=(m=2); equals to n=m=2; Not to use assignment statement as an subexpression to avoid mistakes as follows n=m=2; n=m+2; 36

19 Variables, Expressions, and Uninitialized variable uninitialized desirednumber = minimumnumber + 10; Variable Initialization Garbage value inside Before variables are used In declarations int minimumnumber = 3; double rate = 0.07, time, balance=0.00; double rate(0.07), time, balance(0.00); 37 Variables, Expressions, and 38

20 Variables, Expressions, and More Assignment Statements Variable Operator= Expression; Variable = Variable Operator (Expression); 39 Variables, Expressions, and Assignment Compatibility double to int int intvariable; intvariable = 2.99; double int type mismatch The result depends on compiler Some will issue an error Some will give intvariable the int value 2 40

21 Variables, Expressions, and int to double double doublevariable; doublevariable = 2; int doublevariable=2.0; 41 Variables, Expressions, and char to int int to char char is treated as small integer 42

22 Variables, Expressions, and int intvariable; bool boolvariable; integer to bool boolvariable=intvariable; if intvariable 0 then boolvariable is true else boolvariable is false intvariable=boolvariable if boolvariable is true then intvariable is 1 else intvariable is 0; 43 Variables, Expressions, and Comment Do not place a value of one type in a variable of another type. 44

23 Literals Variables, Expressions, and Considered constants : can t change in program Literal constant int 2, 3, 156 Literal constant double floating-point notation: 2.99, 3.45 Scientific notation: 3.67e17, 2.34E5, 3.49e e17= E5= e-2= Variables, Expressions, and Literal constant char char symbol = Z Literal constant string cout << How many programming language... ; Literal constant bool true false 46

24 Example for retrieving DOS Parameters #include <iostream> using namespace std; int main(int argc, char **argv) { int i; if (argc>0) { cout << "Number of Parameters = " << argc << "\n"; } for (i=0;i<argc;i++) { cout << "Parameter["<< i <<"]=" << argv[i] << "\n"; } } return(0); 47 Example for retrieving DOS Parameters 48

25 Example for retrieving DOS Parameters useful functions int atoi(char *string) float atof(char* string) 49 Variables, Expressions, and Escape Sequences 50

26 Example for escape sequences 51 Example for escape sequences 52

27 Variables, Expressions, and Naming constants Naming your constants Literal constants are OK, but provide little meaning e.g.:seeing 10 in a program, tells nothing about what it represents int BRANCH_COUNT = 10; int WINDOW_COUNT = 10; To avoid values of such variables are changed const int BRANCH_COUNT = 10; const int WINDOW_COUNT = 10; const int BRANCH_COUNT = 10, WINDOW_COUNT = 10; is often called a modifier 53 declared constant Variables, Expressions, and 54

28 Variables, Expressions, and 55 Variables, Expressions, and Arithemetic Operators and Expressions Precedence rules x+y*z=? 56

29 Variables, Expressions, and 57 Variables, Expressions, and 58

30 Variables, Expressions, and Integer and floating-point division Integer division 10/3 = 3 5/2=2 10%3=1 cout << 17 divided by 5 is << (17/5) << \n ; cout << with a remainder of << (17%5) << \n ; output 17 divided by 5 is 3 with a remainder of 2 negative values? 59 Variables, Expressions, and int totalprice1, totalprice2; totalprice1 = 5000 * (feet/5280.0); totalprice2 = 5000 * (feet/5280); if feet=10000; totalprice1=? totalprice2=? 60

31 Variables, Expressions, and totalprice1=5000* /5280.0=9469; totalprice2=10000*10000/5280=10000; 61 Variables, Expressions, and Type Casting totalprice1 = 5000 * (feet/5280.0); double totalprice2 = 5000 * (feet/5280); int Casting for Variables Can add.0 to literals to force precision arithmetic, but what about variables? 62

32 Variables, Expressions, and Static cast double ans = n/static_cast<double>(m); static_cast<double> is like a function that returns an equivalent value of type double static_cast<int>(2.9) is 2 63 Variables, Expressions, and Four kinds of type cast static_cast<type>(expression) Expression const_cast<type>(expression) const dynamic_cast<type>(expression) reinterpret_cast <Type>(Expression) depends on compiler 64

33 Variables, Expressions, and Type coercion ( ) double d = 5; double d=5.0; 65 Variables, Expressions, and Increment and decrement operators Example1 int n=1, m=7; n++; cout << The value of n is changed to << n << \n m--; cout << The value of m is changed to << m << \n ; Output The value of n is changed to 2 The value of m is changed to 6 66

34 Variables, Expressions, and Example2 int n=2; int valueproduced = 2*(n++); cout << valueproduced << \n cout << n << \n ; Output Variables, Expressions, and Example3 int n=2; int valueproduced = 2*(++n); cout << valueproduced << \n cout << n << \n ; Output

35 Variables, Expressions, and Example4 int n=8; int valueproduced = n--; cout << valueproduced << \n cout << n << \n ; Output Variables, Expressions, and Example5 int n=8; int valueproduced = --n; cout << valueproduced << \n cout << n << \n ; Output

36 Variables, Expressions, and Example6 int n=2; int valueproduced = n+ (++n); cout << valueproduced << \n cout << n << \n ; depends on compiler 71 Session Summary Identifiers Variables Assignment Statements More Assignment Statements Assignment Compatibility Literals Escape Sequences Naming Constants 72

37 Session Summary(con t) Arithmetic Operators and Expressions Integer and Floating-Point Division Type Casting Increment and Decrement Operators 73 Console Input/Output Output using cout New lines in output Formatting for numbers with a decimal point Output with cerr Input using cin 74

38 Console Input/Output(con t) I/O objects cin, cout, cerr Defined in the C++ library called <iostream> Must have these lines (called pre-processor directives) near start of file: #include <iostream> using namespace std; Tells C++ to use appropriate library so we can use the I/O objects cin, cout, cerr 75 Console Input/Output(con t) Output using cout What can be outputted? Any data can be outputted to display screen Variables Constants Literals Expressions (which can include all of above) cout << numberofgames << games played. ; 2 values are outputted: value of variable numberofgames, literal string games played. Cascading: multiple values in one cout << is called insertion operation 76

39 Console Input/Output(con t) Example 1 cout << Hello reader.\n << Welcome to C++.\n ; Example 2 cout << numberofgames << games played. ; Example 3 cout << numberofgames; cout << hames played. ; 77 Console Input/Output(con t) Example 4 cout << The total cost is $ << (price + tax); Example 5 cout << firstnumber << << secondnumber; 78

40 Console Input/Output(con t) New Lines in Output New lines in output \n is escape sequence for the char newline A second : endl Examples: cout << Fuel efficiency is << mpg << miles per gallon\n ; cout << you entered << number << endl; End each program with \n or endl 79 Console Input/Output(con t) Formatting Output Formatting numeric values for output Values may not display as you d expect! cout << The price is $ << price << endl; If price (declared double) has value 78.5, you might get: The price is $ or: The price is $78.5 We must explicitly tell C++ how to output numbers in our programs! 80

41 Console Input/Output(con t) Magic Formula to force decimal sizes: cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2); These statements force all future cout ed values: To have exactly two digits after the decimal place Example: cout << The price is $ << price << endl; Now results in the following: The price is $ Console Input/Output(con t) Output with cerr cerr works same as cout Provides mechanism for distinguishing between regular output and error output Re-direct output streams Most systems allow cout and cerr to be redirected to other devices e.g.: line printer, output file, error console, etc. 82

42 Console Input/Output(con t) Input using cin cin for input, cout for output Differences: >> (extraction operator) points opposite Think of it as pointing toward where the data goes Object name cin used instead of cout No literals allowed for cin Must input to a variable you can read in integers, floating-point numbers, or characters 83 Console Input/Output(con t) cin >> num; Waits on-screen for keyboard entry Value entered at keyboard is assigned to num Prompting for Input cout << Enter the number of dragons\n << followed by the number of trolls.\n ; cin >> dragons >> trolls; cin >> dragons >> trolls; 84

43 Console Input/Output(con t) Line breaks in I/O cout << Enter the cost per person : $ ; cin >> costperperson; output Enter the cost per person : $ Enter the cost per person : $ Session Summary Output using cout New lines in output Formatting for numbers with a decimal point Output with cerr Input using cin 86

44 Program Style Bottom-line: Make programs easy to read and modify Comments, two s: // Two slashes indicate entire line is to be ignored /*Delimiters indicates everything between is ignored*/ Both s commonly used Identifier naming ALL_CAPS for constants lowertoupper for variables Most important: MEANINGFUL NAMES! 87 Libraries and Namespaces Libraries and include Directives C++ Standard Libraries #include <Library_Name> Directive to add contents of library file to your program Called preprocessor directive Executes before compiler, and simply copies library file into your program file C++ has many libraries Input/output, math, strings, etc. Some libraries functions are listed in Appendix 4 88

45 Libraries and Namespaces(con t) Namespaces Namespaces defined: Collection of name definitions For now: interested in namespace std Has all standard library definitions we need Examples: #include <iostream> using namespace std; Includes entire standard library of name definitions 89 Libraries and Namespaces(con t) #include <iostream> using std::cin; using std::cout; using std:endl; Can specify just the objects we want 90

46 Chapter Summary C++ is case-sensitive Use meaningful names For variables and constants Variables must be declared before use Should also be initialized Use care in numeric manipulation Precision, parentheses, order of operations #include C++ libraries as needed 91 Chapter Summary(con t) Object cout Used for console output Object cin Used for console input Object cerr Used for error messages Use comments to aid understanding of your program Do not overcomment 92

47 !:op1 Input * p op1 op2 Output cin cout Due date: 2005/3/29 93 r:op1 p:op1 op2