Программа C ++ Calculator — В поисках факториала

Я не могу найти, где я ошибся. Калькулятор работает отлично, но когда я хочу найти факториал данного числа (в качестве оператора используется ‘!’), Я получаю странные ответы, такие как «1» и «59». Может кто-нибудь найти, где я поскользнулся и помочь? Кроме того, извините за длину кода, который я собираюсь загрузить.

#include "Header.h"
class Token {
public:
char kind;        // what kind of token
double value;     // for numbers: a value
Token(char ch)    // make a Token from a char
:kind(ch), value(0) { }
Token(char ch, double val)     // make a Token from a char and a double
:kind(ch), value(val) { }
};class Token_stream {
public:
Token_stream();   // make a Token_stream that reads from cin
Token get();      // get a Token (get() is defined elsewhere)
void putback(Token t);    // put a Token back
private:
bool full;
Token buffer;     // here is where we keep a Token put back using putback()
};// The constructor just sets full to indicate that the buffer is empty:
Token_stream::Token_stream()
:full(false), buffer(0)    // no Token in buffer
{
}// The putback() member function puts its argument back into the Token_stream's buffer:
void Token_stream::putback(Token t)
{
if (full) error("putback() into a full buffer");
buffer = t;       // copy t to buffer
full = true;      // buffer is now full
}Token Token_stream::get()
{
if (full) {       // do we already have a Token ready?
// remove token from buffer
full=false;
return buffer;
}

char ch;
cin >> ch;    // note that >> skips whitespace (space, newline, tab, etc.)

switch (ch) {
case ';':    // for "print"case 'q':    // for "quit"case '(': case ')': case '+': case '-': case '*': case '/': case '{': case '}': case         '!':
return Token(ch);        // let each character represent itself
case '.':
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
{
cin.putback(ch);         // put digit back into the input stream
double val;
cin >> val;              // read a floating-point number
return Token('8',val);   // let '8' represent "a number"}
default:
error("Bad token");
}
}Token_stream ts;        // provides get() and putback()double expression();  // declaration so that primary() can call expression()int factorial (int x)
{
int left = 1;
for (int a = 1; a<=x;++a){
left =a*left;
}
return left;
}

// deal with numbers and parentheses
double primary()
{
Token t = ts.get();
switch (t.kind) {
case '(':    // handle '(' expression ')'
{
double d = expression();
t = ts.get();
if (t.kind != ')') error("')' expected)");
return d;
}
case '{':
{
double d = expression();
t = ts.get();
if (t.kind != '}') error ("'}' expected)");
return d;
}

case '8':
return t.value;
default:
return t.kind;
error("primary expected");
}
}// deal with *, /, and %
double term()
{
double left = primary();
Token t = ts.get();        // get the next token from token stream

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

default:
ts.putback(t);     // put t back into the token stream
return left;
}
}
}// deal with + and -
double expression()
{
double left = term();      // read and evaluate a Term
Token t = ts.get();        // get the next token from token stream

while(true) {
switch(t.kind) {
case '+':
left += term();    // evaluate Term and add
t = ts.get();
break;
case '-':
left -= term();    // evaluate Term and subtract
t = ts.get();
break;
default:
ts.putback(t);     // put t back into the token stream
return left;       // finally: no more + or -: return the answer
}
}
}int main()
try
{
while (cin) {
double val = expression();
Token t = ts.get();

switch(t.kind){
case 'q': cout<<"end of programme";
break;
case ';':        // ';' for "print now"cout << "=" << val << '\n';
break;
default:
ts.putback(t);
val = expression();
}
}
keep_window_open();
}
catch (exception& e) {
cerr << "error: " << e.what() << '\n';
keep_window_open();
return 1;
}
catch (...) {
cerr << "Oops: unknown exception!\n";
keep_window_open();
return 2;
}