Question: CAN YOU EXPLAIN ME HOW TO RUN THIS CODE PLEASE C++ #include #include #include #include using namespace std; enum token { cin_sy, cout_sy, cin_op_sy, cout_op_sy,
CAN YOU EXPLAIN ME HOW TO RUN THIS CODE PLEASE C++
#include
#include
#include
#include
using namespace std;
enum token {
cin_sy, cout_sy, cin_op_sy, cout_op_sy, lparn_sy, rparn_sy, plus_sy, mult_sy, id, int_sy, real_sy,
error_sy, end_source_sy
};
class parser {
private:
ifstream f;
token curr_token;
token check_reserved(string s) {
if (s == "cin") return cin_sy;
else if (s == "cout") return cout_sy;
else return id;
}
token get_token() {
char ch;
string s;
int state = 0;
while (state >= 0 && state <= 11 && !f.eof()) {
switch (state) {
case 0:
f.get(ch);
if (f.eof()) return end_source_sy;
else if (isspace(ch)) {
s = ch; state = 0;
}
else if (isdigit(ch)) {
s = ch; state = 1;
}
else if (ch == '.') {
s = ch; state = 2;
}
else if (isalpha(ch)) {
s = ch; state = 4;
}
else if (ch == '<') state = 5;
else if (ch == '>') state = 6;
else if (ch == '+') state = 7;
else if (ch == '*') state = 8;
else if (ch == '(') state = 9;
else if (ch == ')') state = 10;
else state = 11;
break;
case 1:
f.get(ch);
if (isdigit(ch)) {
s += ch; state = 1;
}
else if (ch == '.') state = 3;
else { f.putback(ch); return int_sy; }
break;
case 2:
f.get(ch);
if (isdigit(ch)) {
s += ch; state = 2;
}
else
{
f.putback(ch);
return real_sy;
}
break;
case 3:
f.get(ch);
if (isdigit(ch)) { s += ch; state = 3; }
else
{
f.putback(ch);
return real_sy;
}
break;
case 4:
f.get(ch);
if (isalnum(ch)) { s + ch; state = 4; }
else
{
f.putback(ch);
return check_reserved(s);
}
break;
case 5:
f.get(ch);
if (ch == '<') return cout_op_sy;
else return error_sy;
break;
case 6:
f.get(ch);
if (ch == '<') return cin_op_sy;
else return error_sy;
break;
case 7:
return plus_sy; break;
case 8:
return mult_sy; break;
case 9:
return lparn_sy; break;
case 10:
return rparn_sy; break;
case 11:
return error_sy; break;
}
}
return end_source_sy;
}
string name (token t) {
switch (t) {
case cin_sy: return "cin token"; break;
case cout_sy: return "cout token"; break;
case cin_op_sy: return ">> token"; break;
case cout_op_sy: return "<< token"; break;
case id: return "identifier"; break;
case int_sy: return "int token"; break;
case real_sy: return "real token"; break;
case plus_sy: return "+ token"; break;
case mult_sy: return "* token"; break;
case lparn_sy: return "( token"; break;
case rparn_sy: return ") token"; break;
case error_sy: return "error token"; break;
case end_source_sy: return "End of file"; break;
}
return "error token";
}
public:
parser (string filename) {
f.open(filename.c_str());
}
~parser () {
f.close();
}
void match(token terminal) {
if (curr_token == terminal)
cout << name(curr_token) << "is matched" << endl;
else
syntax_error(curr_token);
curr_token = get_token();
}
void syntax_error(token terminal) {
cout << name(terminal) << "is not Expected ";
}
void sample_parser() {
curr_token = get_token();
program();
match(end_source_sy);
}
void program() {
if (curr_token == cin_sy) {
match(cin_sy);
match(cin_op_sy);
expr_seq();
}
else if (curr_token == cout_sy) {
match(cout_sy);
match(cout_op_sy);
expr_seq();
}
else
syntax_error(curr_token);
}
void expr_seq () {
expr();
while (curr_token == id || curr_token == int_sy || curr_token == real_sy || curr_token == lparn_sy || curr_token == rparn_sy) {
expr();
}
}
void expr() {
switch (curr_token) {
case id: match(id); break;
case int_sy: match(int_sy); break;
case real_sy: match(real_sy); break;
case lparn_sy:
match(lparn_sy);
if (curr_token == plus_sy) {
match(plus_sy);
expr_seq();
match(rparn_sy);
}
else if (curr_token == mult_sy) {
match(mult_sy);
expr_seq();
match(rparn_sy);
}
else {
syntax_error(curr_token);
}
break;
}
}
};
int main()
{
string name;
cout << "enter file name:"; cin >> name;
parser p(name);
p.sample_parser();
p.~parser();
}
Step by Step Solution
There are 3 Steps involved in it
Get step-by-step solutions from verified subject matter experts
Study Help