bug search in Stroustrup’s calculator 2.1

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 7 Drill 5
Using std_lib_facilities.h by Bjarne Stroustrup.

Drill 5. Do the testing and fix any bugs that you missed when you commented.

//	Philipp Siedler
//	Bjarne Stroustrup's PP
//	Chapter 7 Drill 5

/*
calculator08buggy.cpp
Helpful comments removed.
We have inserted 3 bugs that the compiler will catch and 3 that it won't.
*/

#include "std_lib_facilities.h"

struct Token {
	char kind;
	double value;
	string name;
	Token(char ch) :kind(ch), value(0) { }
	Token(char ch, double val) :kind(ch), value(val) { }
	Token(char ch, string val) :kind(ch), name(val) { } //Error 1: Line missing
};

class Token_stream {
	bool full;
	Token buffer;
public:
	Token_stream() :full(0), buffer(0) { }
	Token get();
	void unget(Token t) { buffer = t; full = true; }
	void ignore(char);
};

const char let = 'L';
const char quit = 'Q';
const char print = ';';
const char number = '8';
const char name = 'a';

Token Token_stream::get()
{
	if (full) {
		full = false; return buffer;
	}
	char ch;
	cin >> ch;
	switch (ch) {
		case '(':
		case ')':
		case '+':
		case '-':
		case '*':
		case '/':
		case '%':
		case ';':
		case '=':
		{
			return Token(ch);
		}
		case '.':
		case '0':
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
		{
			cin.unget();
			double val;
			cin >> val;
			return Token(number, val);
		}
		default:
		{
			if (isalpha(ch)) { //is ch a letter?
				string s;
				s += ch;
				while (cin.get(ch) && (isalpha(ch) || isdigit(ch))) { //reads chars, strings or digits
					s += ch; //Error 2: s = ch;
				}
				cin.unget(); //puts the most recently read character back into the stream
				if (s == "let") return Token(let);
				if (s == "quit") return Token(quit); //Error 2: if (s == "quit") return Token(name);
				return Token(name, s);
			}
			error("Bad token");
			return Token(' '); //Line missing
		}
	}
}

void Token_stream::ignore(char c)
{
	if (full && c == buffer.kind) {
		full = false;
		return;
	}
	full = false;
	char ch;
	while (cin >> ch) {
		if (ch == c) return;
	}
}

struct Variable {
	string name;
	double value;
	Variable(string n, double v) :name(n), value(v) { }
};

vector<Variable> names;

double get_value(string s)
{
	for (int i = 0; i < names.size(); ++i) {
		if (names[i].name == s) {
			return names[i].value;
		}	
	}
	error("get: undefined name ", s);
	return 0.0; //Line missing
}

void set_value(string s, double d)
{
	for (int i = 0; i <= names.size(); ++i) {
		if (names[i].name == s) {
			names[i].value = d;
			return;
		}
	}
	error("set: undefined name ", s);
}

bool is_declared(string s)
{
	for (int i = 0; i<names.size(); ++i) {
		if (names[i].name == s) return true;
	}
	return false;
}

Token_stream ts;

double expression();

double primary()
{
	Token t = ts.get();
	switch (t.kind) {
		case '(':
		{
			double d = expression();
			t = ts.get();
			if (t.kind != ')') error("')' expected"); //Error 3: if (t.kind != ')') error("'(' expected");
			return d; //Line missing
		}
		case '-':
		{
			return -primary();
		}
		case '+':
		{
			return primary();
		}
		case number:
		{
			return t.value;
		}
		case name:
		{
			return get_value(t.name);
		}
		default:
		{
			error("primary expected");
			return 0.0; //Line missing
		}
	}
}

double term()
{
	double left = primary();
	while (true) {
		Token t = ts.get();
		switch (t.kind) {
			case '*':
			{
				left *= primary();
				break;
			}
			case '/':
			{
				double d = primary();
				if (d == 0) error("divide by zero");
				left /= d;
				break;
			}
			default:{
				ts.unget(t);
				return left;
			}
		}
	}
}

double expression()
{
	double left = term();
	while (true) {
		Token t = ts.get();
		switch (t.kind) {
			case '+':
			{
				left += term();
				break;
			}
			case '-':
			{
				left -= term();
				break;
			}
			default:
			{
				ts.unget(t);
				return left;
			}
		}
	}
}

double declaration()
{
	Token t = ts.get();
	if (t.kind != name) { //if (t.kind != 'a')
		error("name expected in declaration");
	}

	string name = t.name;
	if (is_declared(name)) {
		error(name, " declared twice");
	}

	Token t2 = ts.get();
	if (t2.kind != '=') {
		error("= missing in declaration of ", name);
	}
	double d = expression();
	names.push_back(Variable(name, d));
	return d;
}

double statement()
{
	Token t = ts.get();
	switch (t.kind) {
		case let:
		{
			return declaration();
		}
		default:
		{
			ts.unget(t);
			return expression();
		}
	}
}

void clean_up_mess()
{
	ts.ignore(print);
}

const string prompt = "> ";
const string result = "= ";

void calculate()
{
	while (true) try {
		cout << prompt;
		Token t = ts.get();
		while (t.kind == print) {
			t = ts.get();
		}
		if (t.kind == quit) {
			return;
		}
		ts.unget(t);
		cout << result << statement() << endl;
	}
	catch (runtime_error& e) {
		cerr << e.what() << endl;
		clean_up_mess();
	}
}

int main()

try {
	calculate();
	return 0;
}
catch (exception& e) {
	cerr << "exception: " << e.what() << endl;
	char c;
	while (cin >> c&& c != ';');
	return 1;
}
catch (...) {
	cerr << "exception\n";
	char c;
	while (cin >> c && c != ';');
	return 2;
}
Output:
> let x = 5;
= 5
> 6 + x;
= 11
>

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