代码:
1 import java.io.*;
2 public class Main {
3 public static void main (String [] args) throws IOException{
4 char c;
5 c=(char) System.in.read();
6 while(c!='?') {
7 if(c>='A'&&c<='Z') {
8 c+=32;
9 }
10 else if(c>='a'&&c<='z') {
11 c-=32;
12 }
13 else {
14 c=c;
15 }
16 System.out.print(c);
17 c=(char) System.in.read();
18 }
19 }
20 }