B3_1all.cxx

#include <xstream.hxx>#include <ctype.h> enum token_value { NAME, NUMBER, END, PLUS = '+', MINUS = '-', MUL='*', DIV='/', PRINT=';', ASSIGN='=', LP='(', RP=')'}; token_value curr_tok; struct name { char* string; name* next; double value;}; const TBLSZ = 23;name* table[TBLSZ]; int no_of_errors; double error(char* s) { cerr << "error: " << s << "\n"; no_of_errors++; return 1;} extern int strlen(const char*);extern int strcmp(const char*, const char*);extern char* strcpy(char*, const char*); name* look(char* p, int ins = 0){ int ii= 0; char *pp = p; while (*pp) ii = ii<<1 ^ *pp++; if (ii < 0) ii = -ii; ii %= TBLSZ; for (name* n=table [ii]; n; n=n->next) if (strcmp(p,n->string) == 0) return n; if (ins == 0) error("name not found"); name* nn = new name; nn->string = new char[strlen(p) + 1]; strcpy(nn->string,p); nn->value = 1; nn->next = table[ii]; table[ii] = nn; return nn;} inline name* insert(char* s) { return look (s,1); } token_value get_token();double term(); double expr(){ double left = term(); for (;;) switch (curr_tok) { case PLUS: get_token(); left += term(); break; case MINUS: get_token(); left -= term(); break; default: return left; }} double prim(); double term(){ double left = prim(); for (;;) switch (curr_tok) { case MUL: get_token(); left *= prim(); break; case DIV: get_token(); double d = prim(); if (d == 0) return error("divide by o"); left /= d; break; default: return left; }}int number_value;char name_string[80]; double prim(){ switch (curr_tok) { case NUMBER: get_token(); return number_value; case NAME: if (get_token() == ASSIGN) { name* n = insert(name_string); get_token(); n->value = expr(); return n->value; } return look(name_string)->value; case MINUS: get_token(); return -prim(); case LP: get_token(); double e = expr(); if (curr_tok!= RP) return error(") expected"); get_token(); return e; case END: return 1; default: return error ("primary expected"); }} token_value get_token(){ char ch = 0; do { if(!cin.get(ch)) return curr_tok = END; } while (ch!='\n' && isspace(ch)); switch (ch) { case ';': case '\n': cin >> WS; return curr_tok=PRINT; case '*': case '/': case '+': case '-': case '(': case ')': case '=': return curr_tok=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)) { char* p = name_string; *p++ = ch; while (cin.get(ch) && isalnum(ch)) *p++ = ch; cin.putback(ch); *p = 0; return curr_tok=NAME; } error ("bad token"); return curr_tok=PRINT; }} int main(int argc, char* argv[]){ switch (argc) { case 1: break; case 2: cin = *new istream(strlen(argv[1]),argv[1]); break; default: error("too many arguments"); return 1; } // insert predefined names: insert("pi")->value = 3.1415926535897932385; insert("e")->value = 2.7182818284590452354; while (1) { get_token(); if(curr_tok == END) break; if (curr_tok == PRINT) continue; cout << expr() << "\n"; } return no_of_errors;}