原程序如下：
#include<iostream>
#include<cctype>
#include"stack"
using namespace std;

char get_command();
bool do_command(char command,stack<double>& numbers);

int main()
{
stack<double> numbers;
while(do_command(get_command(),numbers));

return 0;
}

//define the function of get_command()
char get_command()
{
char command;
bool waiting=true;
cout<<"select command and press <enter>: ";
while(waiting)
{
cin>>command;
command=tolower(command);
if(command=='?'||command=='+'||command=='-'||command=='*'||command=='/'||command=='='||command=='q')
waiting=false;
else
cout<<"plesae re-enter the right command:"<<endl<<endl;
}

return command;

}

//define the function of do_command
bool do_command(char command,stack<double> &numbers){
double p,q;

switch(command)
{
case '?':
    cout<<"enter a real number:"<<flush;
        cin>>p;
    if(numbers.push(p)==overflow)
        cout<<"the stack is full."<<endl;
    else
        numbers.push(p);
    break;
case '=':
    if(numbers.top(p)==underflow)
        cout<<"stack empty."<<endl;
    else
        cout<<p<<endl;
case '+':
    if(numbers.top(p)==underflow)
        cout<<"stack empty."<<endl;
    else
    {
    numbers.pop();
    if(numbers.top(q)==underflow)
    {    
    cout<<"stack has only one number."<<endl;
    numbers.push(p);
    }   
    else
    {
    numbers.pop();
    if(numbers.push(p+q)==overflow)
        cout<<"stack full:"<<endl;
    }
    }
    break;
case 'q':
    cout<<"calculating finish."<<endl;
    return false;
}
return true;
}

编译错误如下：
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(46) : error C2065: 'overflow' : undeclared identifier
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(46) : error C2120: 'void' illegal with all types
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(52) : error C2661: 'top' : no overloaded function takes 1 parameters
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(52) : error C2065: 'underflow' : undeclared identifier
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(57) : error C2661: 'top' : no overloaded function takes 1 parameters
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(62) : error C2661: 'top' : no overloaded function takes 1 parameters
D:\Program Files\Microsoft Visual Studio\MyProjects\练习的小程序\区分偶数和奇数.cpp(70) : error C2120: 'void' illegal with all types
Error executing cl.exe.
不明白的是我已经把stack文件包含进去了，为什么还说overflow没有定义呢，它应该是已经由error_code定义的枚举类型之一啊 ，大家谁能给解释下，非常感谢！！

头文件有问题。可能是缺空格，
#include<iostream>
#include <iostream>