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 0");

   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;

}