dalao们，这是我的代码，请指教

#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <stack>
#include <cstdio>
#define ll long long
using namespace std;
string s;
vector<ll> a;
stack<char> b;

int more(char c){
	switch(c){
		case '+': return 1;
		case '-': return 1;
		case '*': return 2;
		case '/': return 2;
		case '^': return 3;
		case '(': return 0;
		case ')': return 0;
		default: return -1;
	}
}

ll calculate(ll a, ll b, char op){
	if(op == '+') return a + b;
	if(op == '-') return a - b;
	if(op == '*') return a * b;
	if(op == '/') return a / b;
	if(op == '^'){
		ll ans = 1;
		for(int i = 1; i <= b; i++) ans *= a;
		return ans;
	}
	return (-1 << 30);
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	cin >> s;
	for(int i = 0; i < s.size(); i++){
		if(s[i] >= '0' && s[i] <= '9') a.push_back((ll)(s[i] - '0'));
		else{
			if(b.empty() || s[i] == '^') b.push(s[i]);
			else if(more(s[i]) > more(b.top()) || s[i] == '('){
				b.push(s[i]);
				continue;
			}
			else{
				ll t = more(s[i]);
				if(s[i] == ')'){
					while(!b.empty() && b.top() != '(') a.push_back((ll)(b.top() - '0')), b.pop();
					b.pop();
					continue;
				}
				while(!b.empty() && t <= more(b.top())) a.push_back((ll)(b.top() - '0')), b.pop();
				b.push(s[i]);
			}
		}
	}
	while(!b.empty()) a.push_back((ll)(b.top() - '0')), b.pop();
	
	while(a.size() > 1){
		vector<ll>::iterator it;
		for(it = a.begin(); it != a.end(); it++){
			if(*it < 0 || *it + '0' == 94) cout << (char)(*it + '0');
			else cout << *it;
			cout << ' ';
		}
		cout << "\n";
		for(it = a.begin(); it != a.end(); it++)
			if(*it < 0 || *it + '0' == 94){
				ll tmp = (ll)(calculate(*(it - 2), *(it - 1), (char)(*it + '0')));
				a.insert(it + 1, tmp);
				a.erase(it - 2, it + 1);
				break;
			}
	}
	cout << a[0] << "\n";
    return 0;
}