【求助】缺少函数头什么意思

#include<iostream>
#define SIZE 10
using namespace std;
class CStack
{
    private:
        int position;
        char stk[SIZE];
    public:
        void init(){position=0;}
        char push(char ch);
        char pop();
};
char CStack::push(char ch)
{
    if (position==SIZE)
    {
        cout<<" stack is full"<<endl;
        return 0;
    }
    stk[position++]=ch;
    return ch;
};
char CStack::pop();
{
    if(position==0)
    {
        cout<<"stack is null"<<endl;
        return 0;
    }
    return str[position--];
};
int main()
{
    CStack s;
    s.init();
    char ch;
    while(ch!='!'&&s.push(ch))
        cin>>ch;
    while(ch=s.pop())
        cout<<ch;
    return 0;
}

编译时，出现missing function header (old-style formal list?)  是怎么回事？？？