#include<iostream>
using namespace std;
mian()
{
    bool p=true;
        while(p)
        {
            char ch1,ch2;
            cout<<"请输入小写字母："<<endl;
            cin>>ch1;
            cin.clear();
            cin.sync();
            cout<<"它的大写字母是："<<(char (ch1-32))<<endl;
            cout<<"是否要继续：(y/n)"<<endl;
            cin>>ch2;
            if(ch2='n')p=false;
        }
}

这应该是c++的节奏吧

if(ch2=='n')

mian => main
if(ch2='n') => if(ch2=='n')

很仔细哈