Fundamental of Programming (C)

Transcription

1 Borrowed from lecturer notes by Omid Jafarinezhad Fundamental of Programming (C) Lecturer: Vahid Khodabakhshi CE Fall 97 Lecture 11 Introduction to C++, Object Oriented Programming Department of Computer Engineering 1/19

2 2 C++ Overview C++ was designed at AT&T Bell Labs by Bjarne Stroustrup in the early 80 s nearly 30 years ago! C++ is compatible extension of C that provides: Stronger type-checking Support for data abstraction Support for object-oriented programming Support for generic programming Department of Computer Engineering 2

3 3 C++ Design Goals As with C, run-time efficiency is important Unlike other languages (e.g., Ada, Java, C#, etc.) complicated run-time libraries and virtual machines have not traditionally been required for C++ Note, that there is no language-specific support for concurrency, persistence, or distribution in C++ Compatibility with C libraries & traditional development tools As close to C as possible, but no closer Department of Computer Engineering 3

4 4 C++ Enhancements C++ supports data abstraction & encapsulation e.g., the class mechanism & name spaces C++ supports object-oriented programming features e.g., abstract classes, inheritance, & virtual methods C++ supports generic programming e.g., parameterized types C++ supports sophisticated error handling e.g., exception handling C++ supports identifying an object s type at runtime e.g., Run-Time Type Identification (RTTI) Department of Computer Engineering 4

5 5 Language Features Not Part of C++ Concurrency Persistence Garbage Collection Distribution Department of Computer Engineering 5

6 6 Extensions to C Function Overloading #include <stdio.h> void show(int val) printf("integer: %d\n", val); } void show(double val) printf("double: %lf\n", val); } void show(char const *val) printf("string: %s\n", val); } int main() show(12); show(3.1415); show("hello World!\n"); } Department of Computer Engineering 6

7 7 Extensions to C Function Overloading: Do not use function overloading for functions doing conceptually different tasks. C++ does not allow identically named functions to differ only in their return values. Department of Computer Engineering 7

8 8 Extensions to C Default function arguments #include <stdio.h> int Sum(int a = 1, int b = 4) return a + b;} int main() printf("%d", Sum()); // arguments: printf("%d, Sum(20)); // arguments: printf("%d", Sum(20, 5)); // arguments: // Sum(,6); // Error } Department of Computer Engineering 8

9 9 Extensions to C Default function arguments Default arguments must be known at compiletime since at that moment arguments are supplied to functions. Therefore, the default arguments must be mentioned at the function's declaration, rather than at its implementation: // sample header file extern void two_ints(int a = 1, int b = 4); // code of function in, filename.ccp void two_ints(int a, int b)... } Department of Computer Engineering 9

10 10 Extensions to C #include <iostream> using namespace std; int main() int ival; char sval[30]; std::cout << "Enter a number:\n"; cin >> ival; cout << "And now a string:\n"; cin >> sval; // <<, insertion operator // >>, extraction operator } cout << "The number is: " << ival << "\n" "And the string is: " << sval << '\n'; Department of Computer Engineering 10

11 11 Extensions to C Bool bool bvalue; // true (!=0) or false (0) bool bvalue1 = true; bool bvalue2(false); bool bvalue1 =!true; bool bvalue2(!false); // explicit assignment // implicit assignment // bvalue1 will have the value false // bvalue2 will have the value true bool bvalue = true; // bool bvalue = 30; cout << bvalue << endl; // 1 cout <<!bvalue << std::endl; // 0 if (!bvalue) cout << "The if statement was true" << endl; else cout << "The if statement was false" << endl; Department of Computer Engineering 11

12 12 IOStreams File ifstream (derived from istream) file input ofstream (derived from ostream) output file fstream (derived from iostream). input/output file fstream.h Department of Computer Engineering 12

13 13 IOStreams File output #include <fstream> #include <iostream> // ofstream is used for writing files. // We'll make a file called Sample.dat ofstream outf("sample.dat"); // If we couldn't open the output file stream for writing if (!outf) // Print an error and exit } // We'll write two lines into this file outf << "This is line 1" << endl; outf << "This is line 2" << endl; Department of Computer Engineering 13

14 14 IOStreams Output File #include <fstream> #include ifstream <iostream> returns a 0 if we ve reached the end of the file (EOF) // ifstream is used for reading files // We'll read from a file called Sample.dat ifstream inf("sample.dat"); // If we couldn't open the output file stream for writing if (!inf) // Print an error and exit } // While there's still stuff left to read while (inf) // read stuff from the file into a string and print it std::string strinput; Department of Computer Engineering 14 } inf >> strinput; cout << strinput << endl; getline(inf, strinput);

15 15 Classes and class members struct DateStruct int nmonth; int nday; int nyear; }; // Here is a function to initialize a date void SetDate(DateStruct &sdate, int nmonth, int nday, int nyear) sdate.nmonth = nmonth; sdate.nday = nday; sdate.nyear = nyear; } // In main DateStruct stoday; // Initialize it manually stoday.nmonth = 10; stoday.nday = 14; stoday.nyear = 2040; SetDate(sToday, 10, 14, 2020); Department of Computer Engineering 15

16 16 Classes and class members struct DateStruct int nmonth; int nday; int nyear; }; class Date public: int m_nmonth; int m_nday; int m_nyear; }; Date ctoday; // declare a Object of class Date // Assign values to our members using the member selector operator (.) ctoday.m_nmonth = 10; ctoday.m_nday = 14; ctoday.m_nyear = 2020; Department of Computer Engineering 16

17 17 Access functions and encapsulation class Date private: int m_nmonth; int m_nday; int m_nyear; public: // Getters int GetMonth() return m_nmonth; } int GetDay() return m_nday; } int GetYear() return m_nyear; } }; // Setters void SetMonth(int nmonth) m_nmonth = nmonth; } void SetDay(int nday) m_nday = nday; } void SetYear(int nyear) m_nyear = nyear; } Department of Computer Engineering 17

18 18 Public vs. private access specifiers class Change public: int m_nvalue; }; int main() Change cchange; cchange.m_nvalue = 5; std::cout << cchange.m_nvalue << std::endl; }; class Change private: int m_nvalue; public: void SetValue(int nvalue) m_nvalue = nvalue; } int GetValue() return m_nvalue; } }; int main() Change cchange; cchange.setvalue(5); std::cout << cchange.getvalue() << std::endl; } Department of Computer Engineering 18

19 19 Constructors A constructor is a special kind of class member function that is executed when an object of that class is instantiated Constructors are typically used to initialize member variables of the class to appropriate default values, or to allow the user to easily initialize those member variables to whatever values are desired Constructors have specific rules for how they must be named: Constructors should always have the same name as the class Constructors have no return type (not even void) A constructor that takes no parameters (or has all optional parameters) is called a default constructor Department of Computer Engineering 19