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  1.  
  2. /*
  3. 	calculator08buggy.cpp
  4.  
  5. 	Helpful comments removed.
  6.  
  7. 	We have inserted 3 bugs that the compiler will catch and 3 that it won't.
  8. */
  9.  
  10. //#include "std_lib_facilities.h"
  11. #include <iostream>
  12. #include <string>
  13. #include <vector>
  14. #include <exception>
  15. #include <cctype>
  16.  
  17. using namespace std;
  18.  
  19. struct runtime_error : public exception {
  20. 	string msg;
  21. 	runtime_error(string s) :msg(s) {}
  22. 	~runtime_error() throw() {}
  23. 	const char* what() const throw() { return msg.c_str(); }
  24. };
  25.  
  26. inline void error(string s, string t="") {
  27. 	throw runtime_error(s+" "+t);
  28. }
  29.  
  30. struct Token {
  31. 	char kind;
  32. 	double value;
  33. 	string name;
  34. 	Token(char ch) :kind(ch), value(0) { }
  35. 	Token(char ch, double val) :kind(ch), value(val) { }
  36. 	Token(char ch, string s) :kind(ch), name(s) { }
  37. };
  38.  
  39. class Token_stream {
  40. 	bool full;
  41. 	Token buffer;
  42. public:
  43. 	Token_stream() :full(0), buffer(0) { }
  44.  
  45. 	Token get();
  46. 	void unget(Token t) { buffer=t; full=true; }
  47.  
  48. 	void ignore(char);
  49. };
  50.  
  51. const char let = 'L';
  52. const char quit = 'Q';
  53. const char print = ';';
  54. const char number = '8';
  55. const char name = 'a';
  56.  
  57. Token Token_stream::get()
  58. {
  59. 	if (full) { full=false; return buffer; }
  60. 	char ch;
  61. 	cin >> ch;
  62. 	switch (ch) {
  63. 	case '(':
  64. 	case ')':
  65. 	case '+':
  66. 	case '-':
  67. 	case '*':
  68. 	case '/':
  69. 	case '%':
  70. 	case ';':
  71. 	case '=':
  72. 		return Token(ch);
  73. 	case '.':
  74. 	case '0':
  75. 	case '1':
  76. 	case '2':
  77. 	case '3':
  78. 	case '4':
  79. 	case '5':
  80. 	case '6':
  81. 	case '7':
  82. 	case '8':
  83. 	case '9':
  84. 	{	cin.unget();
  85. 		double val;
  86. 		cin >> val;
  87. 		return Token(number,val);
  88. 	}
  89. 	default:
  90. 		if (isalpha(ch)) {
  91. 			string s;
  92. 			s += ch;
  93. 			while(cin.get(ch) && (isalpha(ch) || isdigit(ch))) s+=ch;
  94. 			cin.unget();
  95. 			if (s == "let") return Token(let);	
  96. 			if (s == "quit") return Token(quit);
  97. 			return Token(name,s);
  98. 		}
  99. 		error("Bad token");
  100. 	}
  101. }
  102.  
  103. void Token_stream::ignore(char c)
  104. {
  105. 	if (full && c==buffer.kind) {
  106. 		full = false;
  107. 		return;
  108. 	}
  109. 	full = false;
  110.  
  111. 	char ch;
  112. 	while (cin>>ch)
  113. 		if (ch==c) return;
  114. }
  115.  
  116. struct Variable {
  117. 	string name;
  118. 	double value;
  119. 	Variable(string n, double v) :name(n), value(v) { }
  120. };
  121.  
  122. vector<Variable> names;	
  123.  
  124. double get_value(string s)
  125. {
  126. 	for (int i = 0; i<names.size(); ++i)
  127. 		if (names[i].name == s) return names[i].value;
  128. 	error("get: undefined name ",s);
  129. }
  130.  
  131. void set_value(string s, double d)
  132. {
  133. 	for (int i = 0; i<=names.size(); ++i)
  134. 		if (names[i].name == s) {
  135. 			names[i].value = d;
  136. 			return;
  137. 		}
  138. 	error("set: undefined name ",s);
  139. }
  140.  
  141. bool is_declared(string s)
  142. {
  143. 	for (int i = 0; i<names.size(); ++i)
  144. 		if (names[i].name == s) return true;
  145. 	return false;
  146. }
  147.  
  148. Token_stream ts;
  149.  
  150. double expression();
  151.  
  152. double primary()
  153. {
  154. 	Token t = ts.get();
  155. 	switch (t.kind) {
  156. 	case '(':
  157. 	{	double d = expression();
  158. 		t = ts.get();
  159. 		if (t.kind != ')') error("'(' expected");
  160. 	}
  161. 	case '-':
  162. 		return - primary();
  163. 	case number:
  164. 		return t.value;
  165. 	case name:
  166. 		return get_value(t.name);
  167. 	default:
  168. 		error("primary expected");
  169. 	}
  170. }
  171.  
  172. double term()
  173. {
  174. 	double left = primary();
  175. 	while(true) {
  176. 		Token t = ts.get();
  177. 		switch(t.kind) {
  178. 		case '*':
  179. 			left *= primary();
  180. 			break;
  181. 		case '/':
  182. 		{	double d = primary();
  183. 			if (d == 0) error("divide by zero");
  184. 			left /= d;
  185. 			break;
  186. 		}
  187. 		default:
  188. 			ts.unget(t);
  189. 			return left;
  190. 		}
  191. 	}
  192. }
  193.  
  194. double expression()
  195. {
  196. 	double left = term();
  197. 	while(true) {
  198. 		Token t = ts.get();
  199. 		switch(t.kind) {
  200. 		case '+':
  201. 			left += term();
  202. 			break;
  203. 		case '-':
  204. 			left -= term();
  205. 			break;
  206. 		default:
  207. 			ts.unget(t);
  208. 			return left;
  209. 		}
  210. 	}
  211. }
  212.  
  213. double declaration()
  214. {
  215. 	Token t = ts.get();
  216. 	if (t.kind != 'a') error ("name expected in declaration");
  217. 	string name = t.name;
  218. 	if (is_declared(name)) error(name, " declared twice");
  219. 	Token t2 = ts.get();
  220. 	if (t2.kind != '=') error("= missing in declaration of " ,name);
  221. 	double d = expression();
  222. 	names.push_back(Variable(name,d));
  223. 	return d;
  224. }
  225.  
  226. double statement()
  227. {
  228. 	Token t = ts.get();
  229. 	switch(t.kind) {
  230. 	case let:
  231. 		return declaration();
  232. 	default:
  233. 		ts.unget(t);
  234. 		return expression();
  235. 	}
  236. }
  237.  
  238. void clean_up_mess()
  239. {
  240. 	ts.ignore(print);
  241. }
  242.  
  243. const string prompt = "> ";
  244. const string result = "= ";
  245.  
  246. void calculate()
  247. {
  248. 	while(true) try {
  249. 		cout << prompt;
  250. 		Token t = ts.get();
  251. 		while (t.kind == print) t=ts.get();
  252. 		if (t.kind == quit) return;
  253. 		ts.unget(t);
  254. 		cout << result << statement() << endl;
  255. 	}
  256. 	catch(runtime_error& e) {
  257. 		cerr << e.what() << endl;
  258. 		clean_up_mess();
  259. 	}
  260. }
  261.  
  262. int main()
  263.  
  264. 	try {
  265. 		calculate();
  266. 		return 0;
  267. 	}
  268. 	catch (exception& e) {
  269. 		cerr << "exception: " << e.what() << endl;
  270. 		char c;
  271. 		while (cin >>c&& c!=';') ;
  272. 		return 1;
  273. 	}
  274. 	catch (...) {
  275. 		cerr << "exception\n";
  276. 		char c;
  277. 		while (cin>>c && c!=';');
  278. 		return 2;
  279. 	}
Success #stdin #stdout 0s 3444KB
comments (?)
stdin
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19+5
let abc=5
let efg=7
abc*efg
quit
stdout
copy 
> = 24
> = 5
> = 7
> = 35
>
https://ideone.com/BTCaJA
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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