今天面試C++，機試面試官看完代碼說代碼結構混亂？

class Token_stream
{
public:
Token_stream() : full(false), buffer(0){};
Token get();
void putback(Token c);

private:
bool full;
Token buffer;
};

void Token_stream::putback(Token t)
{
buffer = t;
full = true;
}

Token Token_stream::get()
{
if (full)
{
full = false;
return buffer;
}
char ch;
cin &>&> ch;
switch (ch)
{
case (:
case ):
case +:
case -:
case *:
case /:
case q:
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.putback(ch);
double val;
cin &>&> val;
return Token(8, val);
default:
error("Bad Token");
}
}

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");
return d;
}

case 8:
return t.value;
default:
error("primary expected");
}
}

double term()
{
double left = primary();
Token t = ts.get();
while (true)
{
switch (t.kind)
{
case *:
left *= primary();
t = ts.get();
break;
case /:
{
double val = primary();
if (val == 0)
error("divide by zero");
left /= val;
t = ts.get();
break;
}
default:
ts.putback(t);
return left;
}
}
}

double expression()
{
double left = term();
Token t = ts.get();
while (true)
{
switch (t.kind)
{
case +:
left += term();
t = ts.get();
break;
case -:
left -= term();
t = ts.get();
break;
default:
ts.putback(t);
return left;
}
}
}

using namespace std;
vector& GetToken(const string str)
{

vector& res;
string buffer;
for(auto ch:str)
{
switch (ch)
{
case +:case -:case *:case /:
if(!buffer.empty())
res.push_back(buffer), buffer.clear();

res.push_back("");
res.back().push_back(ch);
break;
case 0:case 1:case2:case3:case4:case5:case 6:case7:case8:case9:
buffer.push_back(ch);
break;
case : case :
if (!buffer.empty())
res.push_back(buffer),buffer.clear();
break;
default:
throw "error input character.";
}
}
if (!buffer.empty())
res.push_back(buffer);
return res;
}

struct Op;
struct Num;
struct Visitor
{
virtual ~Visitor() = default;
stack& stack;
//這裡不繼承其實可以不用virtual的
virtual void Visit(Op op);
virtual void Visit(Num num);
};
struct Expr
{
virtual ~Expr() = default;
virtual void Accept(Visitor visitor) = 0;
};

struct Op :Expr
{
void Accept(Visitor visitor)override { visitor.Visit(*this); }
explicit Op(char op, shared_ptr& left, shared_ptr& right) :op(op), left(left), right(right){}
char op;
shared_ptr& left, right;
};
struct Num :Expr
{
explicit Num(int num) :num(num) {}
void Accept(Visitor visitor) override { visitor.Visit(*this); }
int num;
};

//Expr = Factor { (+|-) Fcator }
//Factor = num { (*|/) num }
shared_ptr& ParseFactor(const vector& expr, int idx);
shared_ptr& ParseExpr(const vector& expr, int idx)
{
auto res = ParseFactor(expr, idx);
while (idx&(op, res, right);
}
}
return res;
}
shared_ptr& ParseFactor(const vector& expr, int idx)
{
shared_ptr& res = make_shared&(atoi(expr[idx++].c_str()));
while (idx&(atoi(expr[idx++].c_str()));
res = make_shared&(op, res, right);
}
return res;
}
//題目要求用函數指針，我這裡就強行回調一下吧……
void Calculate(std::stack& stack,std::function& operation)
{
auto right = stack.top();
stack.pop();
auto left = stack.top();
stack.top() = operation(left, right);
}
void Visitor::Visit(Op op)
{
op.left-&>Accept(*this);
op.right-&>Accept(*this);
switch (op.op)
{
case +:
Calculate(stack, [](int a, int b) {return a + b; }); break;
case -:
Calculate(stack, [](int a, int b) {return a - b; }); break;
case *:
Calculate(stack, [](int a, int b) {return a*b; }); break;
case /:
Calculate(stack, [](int a, int b) {if (b == 0)throw"cannot devide 0"; return a / b; }); break;
default:
throw "unknown operation";
}
}
void Visitor::Visit(Num num)
{
stack.push(num.num);
}