#include "iostream.h"
char ch[]="why ?";
char &change(int i);
void main()
{
    cout<<ch<<endl;
    cout<<"change(4)"<<change(4)<<endl;
    change(4)='!';
    cout<<ch<<endl;
    cout<<"change(4)"<<change(4)<<endl;
}
char &change(int i )
{
    return ch[i];
}

请高手帮我解释一下这段代码

谢谢