This post series is the Solutions of the Programming — Principles and Practice Using C++ (Second Edition) written by Bjarne Stroustrup
Chapter 6: Writing a Program
Drill
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#include <iostream> #include "../std_lib_facilities.h" using namespace std; double primary(); double term(); double expression(); double primary(); class Token { public: char kind; // what kind of token double value; // for numbers: a value Token(char ch) // make a Token from a char :kind(ch), value(0) { } Token(char ch, double val) // make a Token from a char and a double :kind(ch), value(val) { } }; class Token_stream{ public: Token_stream(); Token get(); void putback(Token t); private: bool full{false}; Token buffer; }; void Token_stream::putback(Token t){ if (full) error("putback() into a full bufer"); buffer = t; full = true; } Token_stream::Token_stream() :full(false), buffer(0) // no Token in buffer { } Token Token_stream::get(){ if (full) { full = false; return buffer; } char ch; cin >> ch; switch (ch) { case ';': case 'q': case '(': case ')': case '+': case '-': case '*': case '/': return Token(ch); case '.': case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': { cin.putback(ch); double val; cin >> val; return Token('8',val); } default: error("Bad Token"); } } Token_stream ts; double primary(){ Token t = ts.get(); switch (t.kind) { case '(': { double d = expression(); t = ts.get(); if (t.kind != ')')error("')' expected"); return d; } case '8': return t.value; default: error("primary expected"); } } double term(){ double left = primary(); Token t = ts.get(); while (true) { switch (t.kind) { case '*': left *= primary(); t = ts.get(); break; case '/': { double d = primary(); if (d==0)error("divide by zero"); left /= d; t = ts.get(); break; } default: ts.putback(t); return left; } } } double expression(){ double left = term(); Token t = ts.get(); while (true){ switch (t.kind) { case '+': left += term(); t = ts.get(); break; case '-': left -= term(); t = ts.get(); break; default: ts.putback(t); return left; } } } int main(int argc, char const *argv[]) { try{ double val = 0; while (cin){ Token t = ts.get(); if (t.kind == 'q') break; if (t.kind == ';') cout << "=" << val << "\n"; else ts.putback(t); val = expression(); } keep_window_open(); } catch (exception& e){ } catch(...){ cerr << "exception \n"; keep_window_open(); return 2; } } |
Example 2
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#include <iostream> #include "../std_lib_facilities.h" using namespace std; double primary(); double term(); double expression(); double primary(); class Token { public: char kind; // what kind of token double value; // for numbers: a value Token(char ch) // make a Token from a char :kind(ch), value(0) { } Token(char ch, double val) // make a Token from a char and a double :kind(ch), value(val) { } }; class Token_stream{ public: Token_stream(); Token get(); void putback(Token t); private: bool full{false}; Token buffer; }; void Token_stream::putback(Token t){ if (full) error("putback() into a full bufer"); buffer = t; full = true; } Token_stream::Token_stream() :full(false), buffer(0) // no Token in buffer { } Token Token_stream::get(){ if (full) { full = false; return buffer; } char ch; cin >> ch; switch (ch) { case ';': case 'q': case '(': case ')': case '{': case '}': case '+': case '-': case '*': case '/': return Token(ch); case '.': case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': { cin.putback(ch); double val; cin >> val; return Token('8',val); } default: error("Bad Token"); } } Token_stream ts; double primary(){ Token t = ts.get(); switch (t.kind) { case '(': case '{': { double d = expression(); t = ts.get(); if (t.kind != ')' && t.kind != '}')error("')' expected"); return d; } case '8': return t.value; default: error("primary expected"); } } double term(){ double left = primary(); Token t = ts.get(); while (true) { switch (t.kind) { case '*': left *= primary(); t = ts.get(); break; case '/': { double d = primary(); if (d==0)error("divide by zero"); left /= d; t = ts.get(); break; } default: ts.putback(t); return left; } } } double expression(){ double left = term(); Token t = ts.get(); while (true){ switch (t.kind) { case '+': left += term(); t = ts.get(); break; case '-': left -= term(); t = ts.get(); break; default: ts.putback(t); return left; } } } int main(int argc, char const *argv[]) { try{ double val = 0; while (cin){ Token t = ts.get(); if (t.kind == 'q') break; if (t.kind == ';') cout << "=" << val << "\n"; else ts.putback(t); val = expression(); } keep_window_open(); } catch (exception& e){ } catch(...){ cerr << "exception \n"; keep_window_open(); return 2; } } |
Example 3
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#include <iostream> #include "../std_lib_facilities.h" using namespace std; double primary(); double term(); double expression(); double primary(); class Token { public: char kind; // what kind of token double value; // for numbers: a value Token(char ch) // make a Token from a char :kind(ch), value(0) { } Token(char ch, double val) // make a Token from a char and a double :kind(ch), value(val) { } }; class Token_stream{ public: Token_stream(); Token get(); void putback(Token t); private: bool full{false}; Token buffer; }; void Token_stream::putback(Token t){ if (full) error("putback() into a full bufer"); buffer = t; full = true; } Token_stream::Token_stream() :full(false), buffer(0) // no Token in buffer { } Token Token_stream::get(){ if (full) { full = false; return buffer; } char ch; cin >> ch; switch (ch) { case ';': case 'q': case '(': case ')': case '{': case '}': case '+': case '-': case '*': case '/': case '!': return Token(ch); case '.': case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': { cin.putback(ch); double val; cin >> val; return Token('8',val); } default: error("Bad Token"); } } Token_stream ts; double primary(){ Token t = ts.get(); switch (t.kind) { case '(': case '{': { double d = expression(); t = ts.get(); if (t.kind != ')' && t.kind != '}')error("')' expected"); return d; } case '8': return t.value; default: error("primary expected"); } } double fact(){ double left = primary(); Token t = ts.get(); while (true) { switch (t.kind) { case '!': { if (left!=ceil(left))error("factorial must be integer"); if (int(left) == 0) left = 1.0; for(int i = int(left-1); i >=1; --i) { left *= i; } t = ts.get(); break; } default: ts.putback(t); return left; } } } double term(){ double left = fact(); Token t = ts.get(); while (true) { switch (t.kind) { case '*': left *= fact(); t = ts.get(); break; case '/': { double d = primary(); if (d==0)error("divide by zero"); left /= d; t = ts.get(); break; } default: ts.putback(t); return left; } } } double expression(){ double left = term(); Token t = ts.get(); while (true){ switch (t.kind) { case '+': left += term(); t = ts.get(); break; case '-': left -= term(); t = ts.get(); break; default: ts.putback(t); return left; } } } int main(int argc, char const *argv[]) { try{ double val = 0; while (cin){ Token t = ts.get(); if (t.kind == 'q') break; if (t.kind == ';') cout << "=" << val << "\n"; else ts.putback(t); val = expression(); } keep_window_open(); } catch (exception& e){ } catch(...){ cerr << "exception \n"; keep_window_open(); return 2; } } |
Example 6
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#include "std_lib_facilities.h" vector<string> nouns; vector<string> verbs; vector<string> conjunctions; void init() { nouns.push_back("birds"); nouns.push_back("fish"); nouns.push_back("C++"); verbs.push_back("rules"); verbs.push_back("fly"); verbs.push_back("swim"); conjunctions.push_back("and"); conjunctions.push_back("or"); conjunctions.push_back("but"); } bool is_noun(string w) { for(int i = 0; i<nouns.size(); ++i) if (w==nouns[i]) return true; return false; } bool is_verb(string w) { for(int i = 0; i<verbs.size(); ++i) if (w==verbs[i]) return true; return false; } bool is_conjunction(string w) { for(int i = 0; i<conjunctions.size(); ++i) if (w==conjunctions[i]) return true; return false; } bool sentence() { string w; cin >> w; if (!is_noun(w)) return false; string w2; cin >> w2; if (!is_verb(w2)) return false; string w3; cin >> w3; if (w3 == ".") return true; if (!is_conjunction(w3)) return false; return sentence(); } int main() try { cout << "enter a sentence of the simplified grammar (terminated by a dot):\n"; init(); while (cin) { bool b = sentence(); if (b) cout << "OK\n"; else cout << "not OK\n"; cout << "Try again: "; } keep_window_open("~"); catch (runtime_error e) { cout << e.what() << '\n'; keep_window_open("~"); } |
Example 7
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#include <iostream> #include "../std_lib_facilities.h" using namespace std; bool primary(); bool term(); bool expression(); bool primary(); class Token { public: char kind; // what kind of token bool value; // for numbers: a value Token(char ch) // make a Token from a char :kind(ch), value(false) { } Token(char ch, bool val) // make a Token from a char and a bool :kind(ch), value(val) { } }; class Token_stream{ public: Token_stream(); Token get(); void putback(Token t); private: bool full{false}; Token buffer; }; void Token_stream::putback(Token t){ if (full) error("putback() into a full bufer"); buffer = t; full = true; } Token_stream::Token_stream() :full(false), buffer(false) // no Token in buffer { } Token Token_stream::get(){ if (full) { full = false; return buffer; } char ch; cin >> ch; switch (ch) { case ';': case 'q': case '!': case '~': case '&': case '|': case '^': return Token(ch); case '.': case '0': case '1': { cin.putback(ch); bool val; cin >> val; return Token('8',val); } default: error("Bad Token"); } } Token_stream ts; bool primary(){ Token t = ts.get(); switch (t.kind) { case '!': case '~': { t = ts.get(); bool d =! t.value; return d; } case '8': return t.value; default: error("primary expected"); } } bool fact(){ bool left = primary(); Token t = ts.get(); while (true) { switch (t.kind) { case '&': { left &= primary(); t = ts.get(); break; } default: ts.putback(t); return left; } } } bool term(){ bool left = fact(); Token t = ts.get(); while (true) { switch (t.kind) { case '^': left ^= fact(); t = ts.get(); break; default: ts.putback(t); return left; } } } bool expression(){ bool left = term(); Token t = ts.get(); while (true){ switch (t.kind) { case '|': left |= term(); t = ts.get(); break; default: ts.putback(t); return left; } } } int main(int argc, char const *argv[]) { try{ bool val = 0; while (cin){ Token t = ts.get(); if (t.kind == 'q') break; if (t.kind == ';') cout << "=" << val << "\n"; else ts.putback(t); val = expression(); } keep_window_open(); } catch (exception& e){ } catch(...){ cerr << "exception \n"; keep_window_open(); return 2; } } |
Example 9
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#include "std_lib_facilities.h" int main() try { vector<int> digit; // collect digits here vector<string> unit; // unit names go here unit.push_back(" ones "); unit.push_back(" tens "); unit.push_back(" hundreds ");; unit.push_back(" thousands "); unit.push_back(" tens of thousands "); unit.push_back(" hundreds of thousands "); unit.push_back(" millions "); unit.push_back(" tens of millions "); unit.push_back(" hundreds of millions "); cout << "Please enter an integer with no more than " << unit.size() << "\ndigits followed by semicolon and a newline: "; char ch; while (cin>>ch) { // remember cin>>ch skips whitespace (this could be simpler written using cin.get(ch) ) if (ch<'0' || '9'<ch) break; // actually: any non-digit acts as a terminator digit.push_back(ch-'0'); } if (digit.size()==0) error("no digits"); if (unit.size()<digit.size()) error("Sorry, cannot handle that many digits"); for (int i =0; i<digit.size(); ++i) cout << char('0'+digit[i]); cout << '\n'; int num = 0; for (int i = 0; i<digit.size(); ++i) { if (digit[i]) cout << digit[i] << unit[digit.size()-i-1]; num = num*10+digit[i]; } cout << "\nthat is " << num << '\n'; keep_window_open("~"); } catch (runtime_error e) { cout << e.what() << '\n'; keep_window_open("~"); } |
Example 10
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#include "std_lib_facilities.h" int factorial(int n) { int fac = 1; while (1<n) { fac *= n; --n; if (fac<1) error("factorial overflow"); } return fac; } int n_permutations(int a, int b) { if (a<b || a<1 || b<1) error("bad permutation sizes"); return factorial(a)/factorial(a-b); } int n_combinations(int a, int b) { return n_permutations(a,b)/factorial(b); } int main() try { cout << "I can calculate the number of combinations and permutations for sets of numbers\n"; cout << "Please enter two numbers (separated by whitespace)\n"; cout << "first the number of elements in the set and then the number of elements in a subset thereof: "; int a, b; if (!(cin>>a>>b)) error("that wasn't two integers"); cout << "enter 'c' to get the number of combinations,\n'p' to get the number of permutations,\nor 'b' to get both: "; bool perm = false; bool comb = false; string s; cin >> s; if (s=="p") perm = true; else if (s=="c") comb = true; else if (s=="b") { perm = true; comb = true; } else error("bad input instruction"); if (perm) cout << "P(" << a << ',' << b << ") = " << n_permutations(a,b) << '\n'; if (comb) cout << "C(" << a << ',' << b << ") = " << n_combinations(a,b) << '\n'; keep_window_open("~"); // For some Windows(tm) setups } catch (runtime_error e) { // this code is to produceerror messages; it will be described in Chapter 5 cout << e.what() << '\n'; keep_window_open("~"); // For some Windows(tm) setups } |