6.S096 Lecture 4 Style and Structure

Transcription

1 6.S096 Lecture 4 Style and Structure Transition from C to C++ Andre Kessler Andre Kessler 6.S096 Lecture 4 Style and Structure 1 / 24

2 Outline 1 Assignment Recap 2 Headers and multiple files 3 Coding style 4 C++ 5 Wrap-up Andre Kessler 6.S096 Lecture 4 Style and Structure 2 / 24

3 Assignment Recap Assignment Recap Floating point Layout of 32-bit floating point numbers in memory. Matrix multiply (1 & 2) Static vs. dynamic allocation Using a data structure Optimizing for the cache Transposition cipher Safely allocating and reading an arbitrary-size string Test data Andre Kessler 6.S096 Lecture 4 Style and Structure 3 / 24

4 Headers and multiple files Header files Separation of declaration and definition // in header (.h) void increment( int *a ); // in source (.c) void increment( int *a ) { ++*a; Include guards (file myheader.h) #ifndef _MYHEADER_H #define _MYHEADER_H void increment( int *a ); //...your header stuff #endif // _MY_HEADER_H Andre Kessler 6.S096 Lecture 4 Style and Structure 4 / 24

5 Coding style Coding style Consistency and clarity above all. Vertical space is precious; horizontal space is good Always using { and even if not needed Again: be consistent. Andre Kessler 6.S096 Lecture 4 Style and Structure 5 / 24

6 The Minimal C Program nothing.c: takes no arguments, does nothing, returns 0 ( exit success ) int main(void) { return 0; 1 To compile: make nothing 2 Previous step produced an executable named nothing 3 To run:./nothing Andre Kessler 6.S096 Lecture 4 Style and Structure 6 / 24

7 The Minimal C++ Program nothing.cpp: takes no arguments, does nothing, returns 0. int main() { return 0; 1 To compile: make nothing 2 Previous step produced an executable named nothing 3 To run:./nothing Andre Kessler 6.S096 Lecture 4 Style and Structure 7 / 24

8 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 int main() { return 0; Andre Kessler 6.S096 Lecture 4 Style and Structure 8 / 24

9 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <cstdio> int main() { return 0; Andre Kessler 6.S096 Lecture 4 Style and Structure 9 / 24

10 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <cstdio> int main() { printf( "Hello, world!\n" ); return 0; Andre Kessler 6.S096 Lecture 4 Style and Structure 10 / 24

11 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <cstdio> int main() { printf( "Hello, world!\n" ); return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello Andre Kessler 6.S096 Lecture 4 Style and Structure 11 / 24

12 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <cstdio> int main() { printf( "Hello, world!\n" ); return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello 4 Hello, world! Andre Kessler 6.S096 Lecture 4 Style and Structure 12 / 24

13 Hello, world! hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <cstdio> int main() { printf( "Hello, world!\n" ); return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello 4 Hello, world! Andre Kessler 6.S096 Lecture 4 Style and Structure 13 / 24

14 Hello, world! done better hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <iostream> int main() { std::cout << "Hello, world!\n"; return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello Andre Kessler 6.S096 Lecture 4 Style and Structure 14 / 24

15 Hello, world! done better hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <iostream> int main() { std::cout << "Hello, world!\n"; return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello 4 Hello, world! Andre Kessler 6.S096 Lecture 4 Style and Structure 15 / 24

16 Hello, world! done better hello.cpp: takes no arguments, prints Hello, world!, returns 0 #include <iostream> int main() { std::cout << "Hello, world!\n"; return 0; 1 To compile: make hello 2 Previous step produced an executable named hello 3 To run:./hello 4 Hello, world! Andre Kessler 6.S096 Lecture 4 Style and Structure 16 / 24

17 What is C++? Multiparadigm programming language Has procedural, object-oriented, functional, generic, and metaprogramming features. Procedural: underneath the surface, C++ is mostly C Object-oriented: classes, encapsulation, inheritance, and polymorphism Generic: template metapgramming, programs that run during compilation Standard Template Library (STL): common idioms, containers, and algorithms Andre Kessler 6.S096 Lecture 4 Style and Structure 17 / 24

18 The Key Differences Generally, can compile C code with a C++ compiler References vs pointers C++ is more strongly typed Stronger notions of casting, static cast<> and so on At the same time, auto variables C++ supports notions of immutability const correctness and constexpr. C++ has extensive abstraction mechanisms Classes and wrapping our memory management Templates template<typename T> Andre Kessler 6.S096 Lecture 4 Style and Structure 18 / 24

19 Immutability and References In addition to the good old pointer, C++ also has a notion of a reference. Let s look at an increment function written in C: void increment( int *a ) { ++*a; // later: call it with int a = 5; increment( &a ); The C++ way: void increment( int &a ) { ++a; // later: call with int a = 5; increment( a ); Andre Kessler 6.S096 Lecture 4 Style and Structure 19 / 24

20 An example of abstraction A safer array // Interface class Array { size_t _size; double *_elem; public: Array( size_t thesize ); ~Array(); inline size_t size() const { return _size; ; double& operator[]( size_t i ); ; Andre Kessler 6.S096 Lecture 4 Style and Structure 20 / 24

21 C++ Resources The C++ Programming Language, 4th ed. by Bjarne Stroustrop Effective C++, More Effective C++, and Effective STL by Scott Meyers Andre Kessler 6.S096 Lecture 4 Style and Structure 21 / 24

22 Examples Time for some examples... Andre Kessler 6.S096 Lecture 4 Style and Structure 22 / 24

23 Wrap-up Second Assignment Second assignment is posted before midnight: three problems total 1000 points linklist (300, C) geom (300, C++) mst (400, C++) Andre Kessler 6.S096 Lecture 4 Style and Structure 23 / 24

24 Wrap-up Wrap-up & Monday Class on Friday Object-oriented programming in C++ Questions? Andre Kessler 6.S096 Lecture 4 Style and Structure 24 / 24

25 MIT OpenCourseWare 6.S096 Effective Programming in C and C++ IAP 2014 For information about citing these materials or our Terms of Use, visit: