c++ primer plus 习题6.1 （cctype，cin.get）

#include<iostream>
#include<cctype>
using namespace std;
int main() {
	char ch,change;
	cout<<"please input:";
	cin.get(ch);
	while(ch != '@'){
		if(!isdigit(ch)){
			if(isupper(ch))
				{
				change=ch+32;
				cout<<change;
				}
			if(islower(ch))
				{	change=ch-32;
					cout<<change;
				}
			if((!isupper(ch))&&(!islower(ch)))
				cout<<ch;
			
		}
		
		cin.get(ch);
	}
	return 0;
}