Страустрап Бьярн
Шрифт:
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[])
{