程序代码：

#include<iostream>
#include<string>
using namespace std;
class Screen{
    public:
    typedef std::string::size_type index;
     char get()const {return contents[cursor];}
       inline    char get(index ht,index wd)const;
    index get_cursor()const;
    Screen(index hght,index wdth,const string &cntnts);
    
    Screen& move(index r,index c);
     Screen& set(char );
        
     Screen& display(ostream &os);
        private:
    std::string contents;
    index cursor;
    index height,width;
};
Screen::Screen(index hght,index wdth,const string &cntnts=" "):contents(cntnts),
cursor(0),height(hght),width(wdth){
    contents.assign(hght*wdth,' ');
    if(cntnts.size()!=0)
    contents.replace(0,cntnts.size(),cntnts);
    
}

char Screen::get(index ht,index wd)const{
    index row=ht*width;
    return contents[row+wd];
}
inline Screen::index Screen::get_cursor() const{
    return cursor;
}
Screen& Screen::set(char c){
    contents[cursor]=c;
    return *this;
}
Screen& Screen::move(index r,index x)
{
    if(r>=height||x>=width){
        cerr<<":invelid row or c"<<endl;
        throw EXIT_FAILURE;
    }
    index row=r*width;
    cursor=row+x;
    return *this;
}
Screen& Screen::display(ostream &os){
string::size_type index=0;
while(index!=contents.size()){
    os<<contents[index];
    if((index+1)%width==0){
        os<<'\n';
    }++index;
}
    return *this;
}

int main(){
    Screen myscreen(5,6,"aaaaa\naaaaa\naaaaa\naaaaa\naaaaa\n");
    myscreen.move(4,0).set('#').display(cout);

    return 0;
}