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;
}