我想实现一个将中缀表达式转化为后缀表达式的程序，请问这是错在哪了？？
#include "stdafx.h"
#include<stack>
#include<iostream>
#include<string>
using namespace std;

int main()
{
    stack<char> op;
    string s;
    cout<<"请输入表达式: ";
    cin>>s;
    istringstream in(s);
    char c;
    while(in>>c)
    {
        if(c=='+'||c=='-'||c=='*'||c=='/')
            op.push(c);
        else if(c==')')
        {
            cout<<op.top()<<" ";
            op.pop();
        }
        else if(c>='0'&&c<='9')
        {
            in.putback(c);
            int n;
            cin>>n;
            cout<<n<<" ";
        }
    }
    while(!op.empty())
    cout<<op.pop()<<endl;
    return 0;
}