New notebooks (solution of task #1 and friendship example)

notebooks/05_Friendship.ipynb

+{"metadata":{"orig_nbformat":4,"language_info":{"codemirror_mode":"text/x-c++src","file_extension":".cpp","mimetype":"text/x-c++src","name":"c++","version":"11"},"kernelspec":{"name":"xcpp11","display_name":"C++11","language":"C++11"}},"nbformat_minor":5,"nbformat":4,"cells":[{"cell_type":"markdown","source":"### Friendship","metadata":{},"id":"e04e0b83-753f-4a58-bce3-3746e7c69650"},{"cell_type":"markdown","source":"* In many situations we tend to make the data members of our classes **private** (or protected in the case of inheritance). \n* If we do so, then no objects of other classes or free-functions have access to them. Not even other objects of the same class.\n* Sometimes this is too restrictive, though. We might need to provide direct access to our members for selected **friends**.\n\n* A typical example is, when we want to overload the ```<<``` operator, to be able to place our object into an output stream.","metadata":{},"id":"6c224ee8-f4c0-495c-8261-6d2c17f845a6"},{"cell_type":"markdown","source":"***\nLet us create a simpe demo class","metadata":{},"id":"ff1a3263-e349-4840-af2f-ad90fde352ac"},{"cell_type":"code","source":"class myTuple {\n\n  int fir;\n  int sec;\n\npublic:\n  myTuple( int fir, int sec ) : fir(fir), sec(sec) {};\n\n};","metadata":{"trusted":true},"execution_count":1,"outputs":[],"id":"cebe299d-3bcc-4a57-af69-8aed41401244"},{"cell_type":"markdown","source":"and try to test-run it","metadata":{},"id":"97622c4c-2eba-47cd-8dbb-c2fe9963dbc3"},{"cell_type":"code","source":"#include <iostream>\n\nint main() {\n\n  myTuple obj( 3, 5 );\n\n  std::cout << \"Pair is: \" << obj << std::endl;\n}\n\nmain();","metadata":{"trusted":true},"execution_count":2,"outputs":[{"name":"stderr","text":"input_line_9:3:28: error: invalid operands to binary expression ('basic_ostream<char, std::char_traits<char> >' and '__cling_N52::myTuple')\n  std::cout << \"Pair is: \" << obj << std::endl;\n  ~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:245:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const void *' for 1st argument; take the address of the argument with &\n      operator<<(const void* __p)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/system_error:217:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const std::error_code' for 2nd argument\n    operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:108:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'std::basic_ostream<char, std::char_traits<char> >::__ostream_type &(*)(std::basic_ostream<char, std::char_traits<char> >::__ostream_type &)' (aka 'basic_ostream<char, std::char_traits<char> > &(*)(basic_ostream<char, std::char_traits<char> > &)') for 1st argument\n      operator<<(__ostream_type& (*__pf)(__ostream_type&))\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:117:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'std::basic_ostream<char, std::char_traits<char> >::__ios_type &(*)(std::basic_ostream<char, std::char_traits<char> >::__ios_type &)' (aka 'basic_ios<char, std::char_traits<char> > &(*)(basic_ios<char, std::char_traits<char> > &)') for 1st argument\n      operator<<(__ios_type& (*__pf)(__ios_type&))\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:127:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'std::ios_base &(*)(std::ios_base &)' for 1st argument\n      operator<<(ios_base& (*__pf) (ios_base&))\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:166:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'long' for 1st argument\n      operator<<(long __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:170:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'unsigned long' for 1st argument\n      operator<<(unsigned long __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:174:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'bool' for 1st argument\n      operator<<(bool __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:178:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'short' for 1st argument\n      operator<<(short __n);\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:181:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'unsigned short' for 1st argument\n      operator<<(unsigned short __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:189:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'int' for 1st argument\n      operator<<(int __n);\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:192:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'unsigned int' for 1st argument\n      operator<<(unsigned int __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:201:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'long long' for 1st argument\n      operator<<(long long __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:205:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'unsigned long long' for 1st argument\n      operator<<(unsigned long long __n)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:220:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'double' for 1st argument\n      operator<<(double __f)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:224:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'float' for 1st argument\n      operator<<(float __f)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:232:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'long double' for 1st argument\n      operator<<(long double __f)\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:276:7: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'std::basic_ostream<char, std::char_traits<char> >::__streambuf_type *' (aka 'basic_streambuf<char, std::char_traits<char> > *') for 1st argument\n      operator<<(__streambuf_type* __sb);\n      ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:511:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'char' for 2nd argument\n    operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:517:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'char' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, char __c)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:523:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'signed char' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, signed char __c)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:528:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'unsigned char' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:565:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const char *' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, const char* __s)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:578:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const signed char *' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:583:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const unsigned char *' for 2nd argument\n    operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/ostream.tcc:321:5: note: candidate function not viable: no known conversion from '__cling_N52::myTuple' to 'const char *' for 2nd argument\n    operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:506:5: note: candidate template ignored: deduced conflicting types for parameter '_CharT' ('char' vs. '__cling_N52::myTuple')\n    operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/basic_string.h:6419:5: note: candidate template ignored: could not match 'basic_string<type-parameter-0-0, type-parameter-0-1, type-parameter-0-2>' against '__cling_N52::myTuple'\n    operator<<(basic_ostream<_CharT, _Traits>& __os,\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:548:5: note: candidate template ignored: could not match 'const _CharT *' against '__cling_N52::myTuple'\n    operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/ostream:691:5: note: candidate template ignored: requirement '__and_<__not_<is_lvalue_reference<basic_ostream<char> &> >, __is_convertible_to_basic_ostream<basic_ostream<char> &>, __is_insertable<__rvalue_ostream_type<basic_ostream<char> &>, const myTuple &> >::value' was not satisfied [with _Ostream = std::basic_ostream<char> &, _Tp = __cling_N52::myTuple]\n    operator<<(_Ostream&& __os, const _Tp& __x)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/shared_ptr.h:66:5: note: candidate template ignored: could not match '__shared_ptr<type-parameter-0-2, _Lp>' against '__cling_N52::myTuple'\n    operator<<(std::basic_ostream<_Ch, _Tr>& __os,\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:413:5: note: candidate template ignored: could not match '_Expr' against 'basic_ostream'\n    _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:344:5: note: expanded from macro '_DEFINE_EXPR_BINARY_OPERATOR'\n    operator _Op(const _Expr<_Dom1, typename _Dom1::value_type>& __v,   \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:413:5: note: candidate template ignored: could not match '_Expr' against 'basic_ostream'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:357:5: note: expanded from macro '_DEFINE_EXPR_BINARY_OPERATOR'\n    operator _Op(const _Expr<_Dom, typename _Dom::value_type>& __v,     \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:413:5: note: candidate template ignored: could not match '_Expr<type-parameter-0-0, typename type-parameter-0-0::value_type>' against '__cling_N52::myTuple'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:370:5: note: expanded from macro '_DEFINE_EXPR_BINARY_OPERATOR'\n    operator _Op(const typename _Dom::value_type& __t,                  \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:413:5: note: candidate template ignored: could not match '_Expr' against 'basic_ostream'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:383:5: note: expanded from macro '_DEFINE_EXPR_BINARY_OPERATOR'\n    operator _Op(const _Expr<_Dom,typename _Dom::value_type>& __e,      \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:413:5: note: candidate template ignored: could not match '_Expr<type-parameter-0-0, typename type-parameter-0-0::value_type>' against '__cling_N52::myTuple'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/bits/valarray_after.h:396:5: note: expanded from macro '_DEFINE_EXPR_BINARY_OPERATOR'\n    operator _Op(const valarray<typename _Dom::value_type>& __v,        \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1193:1: note: candidate template ignored: could not match 'valarray' against 'basic_ostream'\n_DEFINE_BINARY_OPERATOR(<<, __shift_left)\n^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1155:5: note: expanded from macro '_DEFINE_BINARY_OPERATOR'\n    operator _Op(const valarray<_Tp>& __v, const valarray<_Tp>& __w)    \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1193:1: note: candidate template ignored: could not match 'valarray' against 'basic_ostream'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1166:5: note: expanded from macro '_DEFINE_BINARY_OPERATOR'\n    operator _Op(const valarray<_Tp>& __v,                              \\\n    ^\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1193:1: note: candidate template ignored: could not match 'valarray<type-parameter-0-0>' against '__cling_N52::myTuple'\n/srv/conda/envs/notebook/bin/../lib/gcc/../../x86_64-conda-linux-gnu/include/c++/9.4.0/valarray:1177:5: note: expanded from macro '_DEFINE_BINARY_OPERATOR'\n    operator _Op(const typename valarray<_Tp>::value_type& __t,         \\\n    ^\n","output_type":"stream"},{"ename":"Interpreter Error","evalue":"","traceback":["Interpreter Error: "],"output_type":"error"}],"id":"7b80f338-bd48-4699-81aa-fbae245a3a04"},{"cell_type":"markdown","source":"Okay that obviously did not work. Problem is that ```<<``` does not know how to work with objects of type ```myTuple```.\n\n\n* We can fix this by implementing a version of ```<<``` that understands it. \n* Different from our overloading of ```[ ]``` for our ```VectorClass```, we do not do this on the object. Instead we need to overload the free-function that is ```<<```.","metadata":{},"id":"8b28c2a6-533e-478b-91e1-b63270121d6c"},{"cell_type":"code","source":"%%file myTuple.cpp\n\n#include <iostream>\n\nclass myTuple {\n\n  int fir;\n  int sec;\n\npublic:\n  myTuple( int fir, int sec ) : fir(fir), sec(sec) {};\n\n};\n\nstd::ostream& operator << ( std::ostream &os, const myTuple& tup )\n{] for\n    os << \"( \" << tup.fir << \" , \" << tup.sec << \" )\" << std::endl;\n  \n    // necessary for chaining:\n    return os;\n}","metadata":{"trusted":true},"execution_count":2,"outputs":[{"name":"stdout","text":"Overwriting myTuple.cpp\n","output_type":"stream"}],"id":"8dfa7a1c-28d8-4de1-ae19-bdb2a6d3e48e"},{"cell_type":"code","source":"!g++ -Wall -Wextra -c myTuple.cpp","metadata":{"trusted":true},"execution_count":3,"outputs":[{"name":"stdout","text":"myTuple.cpp: In function ‘std::ostream& operator<<(std::ostream&, const myTuple&)’:\nmyTuple.cpp:15:2: error: expected primary-expression before ‘]’ token\n {] for\n  ^\nmyTuple.cpp:14:62: warning: unused parameter ‘tup’ [-Wunused-parameter]\n std::ostream& operator << ( std::ostream &os, const myTuple& tup )\n                                                              ^~~\n","output_type":"stream"}],"id":"25e56a5e-6c64-4d77-9a81-5d808f2b63b3"},{"cell_type":"markdown","source":"* That was to be expected. The attributes ```fir``` and ```sec``` of ```myTuple``` are private.\n* However, we do not want to make them accessible to everyone, just for the sake of one special function/operator.\n* But, we can do so **selectively**, with the friend statement.","metadata":{},"id":"092b284c-9b78-4ea9-9b9a-f43cc5f32612"},{"cell_type":"code","source":"%%file myTuple.cpp\n\n#include <iostream>\n\nclass myTuple {\n\n  int fir;\n  int sec;\n\n  friend std::ostream& operator << ( std::ostream&, const myTuple& );\n\npublic:\n  myTuple( int fir, int sec ) : fir(fir), sec(sec) {};\n\n};\n\nstd::ostream& operator << ( std::ostream &os, const myTuple& tup )\n{\n    os << \"( \" << tup.fir << \" , \" << tup.sec << \" )\" << std::endl;\n  \n    // necessary for chaining:\n    return os;\n}\n\nint main() {\n\n  myTuple obj( 3, 5 );\n\n  std::cout << \"Pair is: \" << obj << std::endl;\n}","metadata":{"trusted":true},"execution_count":10,"outputs":[{"name":"stdout","text":"Overwriting myTuple.cpp\n","output_type":"stream"}],"id":"ff341d41-7aa2-4f87-92f2-e189dd448d68"},{"cell_type":"code","source":"!g++ -Wall -Wextra myTuple.cpp","metadata":{"trusted":true},"execution_count":11,"outputs":[],"id":"c8560f81-10ef-4203-b3f3-8046255be25a"},{"cell_type":"code","source":"!./a.out","metadata":{"trusted":true},"execution_count":12,"outputs":[{"name":"stdout","text":"Pair is: ( 3 , 5 )\n\n","output_type":"stream"}],"id":"6a5f1cb3-7891-4cb8-b8ce-d3f6aa996ecc"},{"cell_type":"code","source":"","metadata":{},"execution_count":null,"outputs":[],"id":"94e6f340-7a06-4c59-8889-5088e41712f2"}]}
\ No newline at end of file

notebooks/Task#1.ipynb

+{"metadata":{"orig_nbformat":4,"language_info":{"codemirror_mode":"text/x-c++src","file_extension":".cpp","mimetype":"text/x-c++src","name":"c++","version":"17"},"kernelspec":{"name":"xcpp17","display_name":"C++17","language":"C++17"}},"nbformat_minor":5,"nbformat":4,"cells":[{"cell_type":"markdown","source":"### Task #1\n\nIn this task we want to further extend our ```VectorClass``` class. Specifically we would like add two methods and answer a question concerning ```VectorClass::print()```: \n 1. Implement missing body of VectorClass::scale()\n 1. Implement VectorClass::innerProduct(), how should the header look like?\n 1. What happens, when we call myVec.print() without arguments in main?","metadata":{},"id":"5b54f8c4-59a0-4a5a-a15c-021d20ae3d22"},{"cell_type":"markdown","source":"Let us start with (2). How should the interface for ```innerProduct()``` look like?","metadata":{},"id":"45df3877-fe76-43fd-afeb-dd4de9d969c3"},{"cell_type":"code","source":"\n\n\n\n\n\n\n\n\n\n\n\n\n\n","metadata":{},"execution_count":null,"outputs":[],"id":"a217056c-feec-46b7-aaac-5d673e57c53f"},{"cell_type":"markdown","source":"- Our vectors store entries of type ```double```. Thus, that would be a fitting return type for the value of the computed Euclidean inner product. *We could hand the result back via a parameter, too. But that is probably less convenient here.*\n- We need two vectors for the operation, so the second one should be an input argument. But:\n  - Use a reference to avoid copy generation.\n  - Not going to change the vector, so that could be const.\n- Method will not change the VectorClass object itself either, so the method could be marked const, too.\n\nSo we end up with:\n\n**``` double innerProduct( const VectorClass& second ) const;```**","metadata":{},"id":"0c933e9f-554b-455c-b023-7f8e533e75dd"},{"cell_type":"markdown","source":"***\nOkay, so below is our extended ```VectorClass``` minus the actual implementation of the two methods:","metadata":{},"id":"274868db-03d2-4c69-99e2-cbedc0f31960"},{"cell_type":"code","source":"#include <iostream>\n#include <cassert>\n\nclass VectorClass{\n    \npublic:\n\n  // ------------------------------------------------\n  // User should specify dimension at object creation\n  // ------------------------------------------------\n  VectorClass( unsigned int dim ) : dim_(dim) {\n            \n    // don't allow vectors with zero dimension\n    assert( dim_ > 0 );\n\n    // allocate memory (will throw an exception, if it fails)\n    vec_ = new double[ dim_ ];\n            \n    // be talkative ;-)\n    std::cout << \"An instance of VectorClass was generated. dim_ = \" << dim_ << std::endl;\n  }\n\n  // ----------------------------------------------------------\n  // Don't allow the default constructor\n  // [prior to C++11 you would solve this by making it private]\n  // ----------------------------------------------------------\n  VectorClass() = delete;\n\n  // ----------------------------------------------------------\n  // Don't allow the following default copy constructor either    \n  // ----------------------------------------------------------\n  VectorClass( VectorClass &other ) = delete;\n \n  // ----------------------------------------------------------\n  // We need to implement a destructor to free the dynamic memory again,\n  // otherwise we easily produce memory leaks\n  // ----------------------------------------------------------\n  ~VectorClass() {\n    std::cout << \"Going to delete memory starting at address \" << vec_ << std::endl;\n          \n    delete[] vec_;\n    std::cout << \"An instance of VectorClass was destroyed and \"\n              << dim_ * sizeof(double)\n              << \" bytes freed.\" << std::endl;\n  }\n\n  // ----------------------------------------------------------\n  // provide access to the vector's dimension\n  // ----------------------------------------------------------\n  unsigned int getDim() const { return dim_; }\n    \n  // ----------------------------------------------------------\n  // overload the [] for accessing individual entries\n  // ----------------------------------------------------------\n  double& operator[] ( unsigned int index ) {\n    assert( index != 0 && index <= dim_ );\n    return vec_[index-1];\n  }\n\n  const double& operator[] ( unsigned int index ) const {\n    assert( index != 0 && index <= dim_ );\n    return vec_[index-1];\n  }\n\n  // ----------------------------------------------------------------------\n  // pretty print vector to given output stream (default will be std::cout)\n  // ----------------------------------------------------------------------\n  void print( std::ostream &os = std::cout ) const {\n    os << \"(\";\n    for( unsigned int k = 0; k < dim_-1; k++ ) {\n      os << vec_[k] << \", \";\n    }\n    os << vec_[dim_-1] << \")\" << std::endl;\n  }\n    \n  // ----------------------------\n  // scale vector with a constant\n  // ----------------------------\n  void scale( double factor );\n    \n  // ----------------------------------------------\n  // compute Euclidean inner product of two vectors\n  // ----------------------------------------------\n  double innerProduct( const VectorClass& second ) const;\n    \n  // ----------------------------------------------------------------------\n  // add to vectors together (that's actually a little bit tricky,\n  // due to the question \"where to put the result?\"\n  // for the moment leave it with adding another vector to the one on which\n  // the method is called.\n  // ----------------------------------------------------------------------\n  void add( const VectorClass& other ) {\n\n    // make sure that input vector has correct length\n    assert( other.getDim() == dim_ );\n    // for( unsigned int k = 0; k < dim_; k++ ) {\n    //     vec_[k] += other[k+1];\n    // }\n    for( unsigned int k = 1; k <= dim_; k++ ) {\n      this->operator[](k) += other[k];\n    }\n  }\n    \nprivate:\n  unsigned int dim_;   // dimension of vector\n  double* vec_;        // entries of vector\n\n};","metadata":{"trusted":true},"execution_count":1,"outputs":[],"id":"2bcf89a4-e232-47f8-afe2-a88897f13a52"},{"cell_type":"markdown","source":"***\nNow let us implement ```scale()```","metadata":{},"id":"7ab16ac5-7f91-43cc-9a68-2e8a52dd3058"},{"cell_type":"code","source":"void VectorClass::scale( double factor ) {\n \n    for( unsigned int k = 0; k < dim_; k++ ) {\n      vec_[k] *= factor;\n    }\n    \n}","metadata":{"trusted":true},"execution_count":2,"outputs":[],"id":"816a0c45-6ff9-4d67-97e7-b076bd23526d"},{"cell_type":"markdown","source":"and ```innerProduct()```","metadata":{},"id":"c84995ae-c03e-41e7-a060-f5d7b4382c55"},{"cell_type":"code","source":"double VectorClass::innerProduct( const VectorClass& second ) const {\n\n    double prod = 0.0;\n\n    for( unsigned int k = 0; k < dim_; k++ ) {\n      prod += vec_[k] * second[k+1];               // remember our overloading of [], vec_[k] = this->operator[k+1]\n    }\n\n    return prod;\n\n}   ","metadata":{"trusted":true},"execution_count":3,"outputs":[],"id":"139b925e-5b80-4ea8-80e9-ffb1ace29ffc"},{"cell_type":"markdown","source":"A question on ```scale()```: Why did we not make it **```void scale( const double factor ) const```** ?","metadata":{},"id":"0b36c822-eae1-4b20-b7ad-1ff1938b723c"},{"cell_type":"markdown","source":"\n\n\n\n\n\n\n\n\n\n\n\n\n","metadata":{},"id":"80b43239-51ec-4b63-af94-ce4e59fc6cc2"},{"cell_type":"markdown","source":"There are two aspects to this:\n1. The method itself cannot be marked ```const``` as it changes the state of our object, by changing values inside ```vec_```.\n1. We could mark ```factor``` as ```const```, but\n   - It is a local variable, so changes to factor would have no effect outside the body of scale() anyhow.\n   - For a basic datatype like double we are not sure if it would allow the compiler to perform some extra optimisations.\n   - Finally it is more a question of whether you think it is worth the extra effort of marking it this way.","metadata":{},"id":"9e17a14b-096c-4abb-b806-8fedc733c9fc"},{"cell_type":"markdown","source":"***\nBelow follows our test-driver that should run through now the extension was completed","metadata":{},"id":"b44bb8cd-35c0-45d5-8c0e-ee80fed8d018"},{"cell_type":"code","source":"#include <cmath>    // for using std::sqrt() below\n\nint main() {\n\n  const unsigned int dim = 10;\n  \n  // set up 1st vector\n  VectorClass myVec( dim );\n  for( unsigned int idx = 1; idx <= dim; idx ++ ) {\n    myVec[ idx ] = static_cast<double>( dim - idx + 1 );\n  }\n  myVec.print( std::cout );\n    \n  // set up 2nd vector\n  VectorClass other( dim );\n  for( unsigned int idx = 1; idx <= dim; idx ++ ) {\n    other[ idx ] = static_cast<double>( idx );\n  }\n  other.print( std::cout );\n\n  // add the 2nd to the 1st\n  std::cout << \"\\nAdding both vectors gives: \";\n  myVec.add( other );\n  myVec.print();\n\n  // now scale second vector by 0.5\n  std::cout << \"\\nScaling the vector: \";\n  other.print();\n  std::cout << \"by 0.5 gives: \";\n  other.scale( 0.5 );\n  other.print();\n  std::cout << std::endl;\n\n  // compute the norm of the following vector\n  VectorClass vec( 2 );\n  vec[1] = 3.0;\n  vec[2] = -4.0;\n  double norm = vec.innerProduct( vec );\n  norm = std::sqrt( norm );\n  std::cout << \"Norm of vector \";\n  vec.print();\n  std::cout << \"is \" << norm << std::endl;\n    \n  std::cout << std::endl;\n  // now destructors will be called\n}","metadata":{"trusted":true},"execution_count":8,"outputs":[],"id":"6fd51fae-99a1-476c-ad9f-59529b88811e"},{"cell_type":"code","source":"main();","metadata":{"trusted":true},"execution_count":7,"outputs":[{"name":"stdout","text":"An instance of VectorClass was generated. dim_ = 10\n(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)\nAn instance of VectorClass was generated. dim_ = 10\n(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\n\nAdding both vectors gives: (11, 11, 11, 11, 11, 11, 11, 11, 11, 11)\n\nScaling the vector: (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)\nby 0.5 gives: (0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5)\n\nAn instance of VectorClass was generated. dim_ = 2\nNorm of vector (3, -4)\nis 5\n\nGoing to delete memory starting at address 0x556e84d85490\nAn instance of VectorClass was destroyed and 16 bytes freed.\nGoing to delete memory starting at address 0x556e84b3ee40\nAn instance of VectorClass was destroyed and 80 bytes freed.\nGoing to delete memory starting at address 0x556e84b446c0\nAn instance of VectorClass was destroyed and 80 bytes freed.\n","output_type":"stream"}],"id":"9c827691-afe9-4cfb-b71d-4f01bccd09c2"},{"cell_type":"markdown","source":"***\nFinally, we need to answer question (3).\n\n * In our driver we just called ```vec.print()``` without providing an output stream as argument. How did that work?\n\n * At some point we change the implementation of VectorClass::print() to have a **default value** for its os argument:  \n     **```void print( std::ostream &os = std::cout ) const```**\n     \n * Thus, if no argument is given, the compiler will automatically insert ```std::cout```.","metadata":{},"id":"067df258-3921-4328-bd14-cec60a4a02d8"},{"cell_type":"markdown","source":"#### Language Overview \n| language | optional arguments (w/ default values) | passing via keyword |\n|:---------| :-------------------------------------:|:-------------------:|\n| C        | no (only via workarounds)              | no                  |\n| C++      | yes                                    | no                  |\n| Fortran  | yes                                    | yes                 |\n| Python   | yes                                    | yes                 |\n\nPassing via keyword means, that we can set some arguments explicitely by a **name=value** pair.  \nPython example: ```print ('comma', 'separated', 'words', sep=', ')```  \n\n#### Optional Arguments in C++\n* In C++ there are some restrictions on the use of optional arguments.\n* Some of these are related to the fact that *passing via keyword* is not supported.\n* Rules are:\n  - optional arguments must follow the 'regular' ones\n  - if you do not supply a value for one optional argument, then you must also skip all arguments after that one","metadata":{},"id":"a59f1813-b205-439d-bb91-986e51df9336"},{"cell_type":"code","source":"#include <iostream>\n#include <string>\n\nvoid showVals( int a, int b = 2, double x = 1.0, std::string m = \"go\" ) {\n  std::cout << \"(\"\n            << a << \", \"\n            << b << \", \"\n            << x << \", \"\n            << m << \")\" << std::endl;\n}","metadata":{"trusted":true},"execution_count":1,"outputs":[],"id":"aa9570b3-2a56-4b23-acaa-48c28a781870"},{"cell_type":"code","source":"int main() {\n\n  showVals( 3 );\n  showVals( 5, 3 );\n  showVals( 1, 2, 3 );\n  showVals( 4, 5, 6, \"Alte Gags\" );\n\n  // showVals( 3, \"Polizei\" ); will not compile\n\n}\n\nmain();","metadata":{"trusted":true},"execution_count":4,"outputs":[{"name":"stdout","text":"(3, 2, 1, go)\n(5, 3, 1, go)\n(1, 2, 3, go)\n(4, 5, 6, Alte Gags)\n","output_type":"stream"}],"id":"ae9ceb03-fe74-4774-9d9c-b3d6d63d6710"},{"cell_type":"code","source":"","metadata":{},"execution_count":null,"outputs":[],"id":"c5eb79ba-2885-4de6-9f14-692c810222d5"}]}
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