/* Reference Chapter 6: "The C++ Programming Language", Special Edition. Bjarne Stroustrup,Addison-Wesley Pub Co; 3 edition (February 15, 2000) ISBN: 0201700735 */ #include #include #include #include #include using namespace std; enum Token_value { NAME, NUMBER, END, INC, DEC, PLUS='+', MINUS='-', MUL='*', DIV='/', PRINT=';', ASSIGN='=', LP='(', RP=')' }; Token_value curr_tok = PRINT; double number_value; string string_value; double expr(bool ); double term(bool ); double error(const string&); double prim(bool ); Token_value get_token(); map table; double expr(bool get) { double left = term(get); for(;;) switch(curr_tok) { case PLUS: left += term(true); break; case MINUS: left -= term(true); break; default: return left; } } double term(bool get) { double left = prim(get); for(;;) switch(curr_tok) { case MUL: left *= prim(true); break; case DIV: if (double d = prim(true)) { left /=d; break; } return error("divide by 0"); default: return left; } } double prim(bool get) { if(get) get_token(); switch(curr_tok) { case NUMBER: { double v = number_value; get_token(); return v; } case NAME: { double& v = table[string_value]; get_token(); if (curr_tok == ASSIGN) v = expr(true); if (curr_tok == INC) //r++; v = v+1; if (curr_tok == DEC) //r++; v = v-1; return v; } case INC: return prim(true)+1; case DEC: return prim(true)-1; case MINUS: return -prim(true); case LP: { double e=expr(true); if(curr_tok != RP) return error(" ')' expected"); get_token(); return e; } default: return error("primary expected"); } } Token_value get_token() { char ch; do { if(!cin.get(ch)) return curr_tok = END; } while(ch!='\n' && isspace(ch)); switch(ch) { case ';': case '\n': return curr_tok=PRINT; case 0: return curr_tok=END; case '+': // added for ++name and name++ { char c; if ( cin.get(c) && c == '+' ) return curr_tok=INC; cin.putback(c); return curr_tok=Token_value(ch); } case '-': { char c; if ( cin.get(c) && c == '-' ) return curr_tok=DEC; cin.putback(c); return curr_tok=Token_value(ch); } case '*': case '/': case '(': case ')': case '=': return curr_tok=Token_value(ch); case '0':case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': case '.': cin.putback(ch); cin >> number_value; return curr_tok=NUMBER; default: if (isalpha(ch)){ string_value=ch; while(cin.get(ch) && isalnum(ch)) string_value.push_back(ch); cin.putback(ch); return curr_tok=NAME; } error("bad token"); return curr_tok=PRINT; } } int no_of_errors; double error(const string& s) { no_of_errors++; cerr << "error: " << s << '\n'; return 1; } istream* input; int main(int argc, char* argv[]) { switch(argc) { case 1: input = &cin; break; case 2: input = new istringstream(argv[1]); break; default: error("too man arguments"); return 1; } table["pi"] = 3.1415926535897932385; table["e"] = 2.718281818284590452354; while(cin) { get_token(); if( curr_tok == END) break; if( curr_tok == PRINT) continue; cout << expr(false) << '\n'; } if(input != &cin) delete input; return no_of_errors; }