file input calculator

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 10 Exercise 10
Using std_lib_facilities.h by Bjarne Stroustrup.

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PPP
// Chapter 10 Exercise 10

#include "std_lib_facilities.h"

const char let = ‘#’;
const char quitProg = ‘Q’;
const char print = ‘;’;
const char number = ‘8’;
const char name = ‘a’;
const char sqroot = ‘S’;
const char power = ‘P’;
const char constant = ‘C’;
const char reset = ‘R’;
const char help = ‘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) { }
};

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

Token Token_stream::get(ifstream& ist)
{
/*
if (full) {
full = false;
return buffer;
}

char ch;
ist >> ch;
*/

if (full) {
full = false; return buffer;
}
char ch;
ist.get(ch);

while (isspace(ch)) {
if (ch == ‘\n’) return Token(print); // if newline detected, return print Token
ist.get(ch);
}

switch (ch) {
case ‘(‘:
case ‘)’:
case ‘+’:
case ‘-‘:
case ‘*’:
case ‘/’:
case ‘%’:
case ‘;’:
case ‘=’:
case ‘k’:
case ‘,’:
{
return Token(ch);
}
case ‘#’:
{
return Token(let);
}
case ‘.’:
case ‘0’:
case ‘1’:
case ‘2’:
case ‘3’:
case ‘4’:
case ‘5’:
case ‘6’:
case ‘7’:
case ‘8’:
case ‘9’:
{
ist.unget();
double val;
ist >> val;
return Token(number, val);
}
default:
{
if (isalpha(ch) || ch == ‘_’) { //is ch a letter?
string s;
s += ch;
while (ist.get(ch) && (isalpha(ch) || isdigit(ch) || ch == ‘_’)) { //reads chars, strings or digits
s += ch;
}
ist.unget(); //puts the most recently read character back into the stream
if (s == "quit") return Token(quitProg);
if (s == "sqrt") return Token(sqroot);
if (s == "pow") return Token(power);
if (s == "const") return Token(constant);
if (s == "reset") return Token(reset);
if (s == "help" || s == "Help") return Token(help);
return Token(name, s);
}
error("Bad token");
return Token(‘ ‘);
}
}
}

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;
bool immutable;
Variable(string n, double v, bool i) :name(n), value(v), immutable(i) { }
};

class Symbol_table {
public:
vector<Variable> var_table;
double get(string);
void set(string, double);
bool is_declared(string);
double declare(char, ifstream& ist);
bool is_immutable(string);
};

Token_stream ts;
double expression(ifstream& ist);
double primary(ifstream& ist);

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

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

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

double Symbol_table::declare(char kind, ifstream& ist)
{
Token t = ts.get(ist);
if (t.kind != name) {
error("name expected in declaration");
}

string name = t.name;
if (kind == let || kind == constant) {
if (is_declared(name)) error(name, " declared twice");
}
else if (kind == reset) {
if (!is_declared(name))
error(name, " has not been declared");
if (is_immutable(name))
error(name, " is a constant");
}
else {
error("unknown statement");
}

Token t2 = ts.get(ist);
if (t2.kind != ‘=’) error("= missing in declaration of ", name);
double d = expression(ist);
if (is_declared(name))
set(name, d);
else
var_table.push_back(Variable(name, d, (kind == constant)));
return d;
}

bool Symbol_table::is_immutable(string s)
{
for (int i = 0; i<int(var_table.size()); ++i)
if (var_table[i].name == s && var_table[i].immutable) return true;
return false;
}

double pow_function(Token _t, ifstream& ist) {
_t = ts.get(ist);
if (_t.kind != ‘(‘) {
error("'(‘ expected");
}

double x = expression(ist);

_t = ts.get(ist);
if (_t.kind != ‘,’) {
error("’,’ expected");
}

double n = expression(ist);
_t = ts.get(ist);
if (_t.kind == ‘)’) {
return pow(x, n);
}
else {
error("Expected ‘)’");
}
}

double sqrt_function(Token _t, ifstream& ist) {
_t = ts.get(ist);
if (_t.kind != ‘(‘) {
error("'(‘ expected");
}
ts.unget(_t);
double d = primary(ist);
if (d < 0.0) {
error("negative square root");
}
return sqrt(d);
}

Symbol_table st;

double primary(ifstream& ist)
{
Token t = ts.get(ist);
switch (t.kind) {
case ‘(‘:
{
double d = expression(ist);
t = ts.get(ist);
if (t.kind != ‘)’) error("’)’ expected");
return d;
}
case ‘-‘:
{
return -primary(ist);
}
case ‘+’:
{
return primary(ist);
}
case number:
{
return t.value;
}
case sqroot:
{
return sqrt_function(t, ist);
}
case power:
{
return pow_function(t, ist);
}
case name:
{
return st.get(t.name);
}
default:
{
error("primary expected");
return 0.0;
}
}
}

double term(ifstream& ist)
{
double left = primary(ist);
while (true) {
Token t = ts.get(ist);
switch (t.kind) {
case ‘k’:
{
left *= 1000;
break;
}
case ‘*’:
{
left *= primary(ist);
break;
}
case ‘/’:
{
double d = primary(ist);
if (d == 0) error("divide by zero");
left /= d;
break;
}
case ‘%’:
{
int i1 = narrow_cast<int>(left);
int i2 = narrow_cast<int>(primary(ist));
if (i2 == 0) error("%: divide by zero");
left = i1%i2;
break;
}

default: {
ts.unget(t);
return left;
}
}
}
}

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

double statement(ifstream& ist)
{
Token t = ts.get(ist);
double d;
if (t.kind == let || t.kind == reset || t.kind == constant) {
d = st.declare(t.kind, ist);
}
else {
ts.unget(t);
d = expression(ist);
}
t = ts.get(ist);
if (t.kind != print) {
error("Missing terminator");
}

return d;
}

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

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

void calculate(ifstream& ist, ofstream& ost)
{
ost << "Welcome to my calculator.\n"
<< "Just hit enter or ; at the end of your function to calculate.\n"
<< "Enter help or Help for help or quit to exit the program.\n";
while (ist) try {
ost << prompt;
Token t = ts.get(ist);
while (t.kind == print) {
t = ts.get(ist);
}
if (t.kind == help) {
ost << "You can use / *-+operators.\n"
<< "Declaring variables using #, for example: # x = 5.\n";
}
else {
if (t.kind == quitProg) {
return;
}
ts.unget(t);
ost << result << statement(ist) << endl;
break;
}
}
catch (runtime_error& e) {
ost << e.what() << endl;
clean_up_mess();
}
}

int main()

try {

string iname = "input/ch10_p378_10_input.txt";
string oname = "output/ch10_p378_10_output.txt";
ifstream ist{ iname };
ofstream ost{ oname };

calculate(ist, ost);
keep_window_open();
//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;
}
[/code]

Output:
Please enter a character to exit
Input-File: ch10_p378_10_input.txt
6+5;
Output-File: ch10_p378_10_output.txt
Welcome to my calculator.
Just hit enter or ; at the end of your function to calculate.
Enter help or Help for help or quit to exit the program.
> = 11

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