以下程序段运行后，输入：ABCdef，输出应为
char ch; while ((ch = getchar ()) != '\n') { if (ch >= 'A' && ch <= 'Z') ch = ch + 32; else if (ch >= 'a' && ch <= 'z') ch = ch - 32; cout << ch; }
ABCdef
abcdef
ABCDEF
abcDEF
