这两个函数具体有什么区别，能帮我分析一下吗

能帮我分析一下  char &replace(int k){return s[k];}  和  char *rep(int k) {return &s[k];}的区别吗


#include<iostream>
using namespace std;
char s[80]="Hello World";
char &replace(int k){return s[k];}
char *rep(int k) {return &s[k];}
void main(){
    replace(11)='!';

    cout<<rep(0)<<endl;
    cout<<replace(11)<<endl;

    *rep(5)='+';

    cout<<rep(0)<<endl;
    cout<<replace(6)<<endl;
}