第六章例6-5

#include<stdio.h>
int main(void)
{
char ch;

printf("input characters:");
ch=getchar( );

while(ch!='\n'){
  if(ch>='A'&&ch<='Z')
   ch=ch-'A'+'a';
  else if(ch>='a'&&ch<='z')
   ch=ch-'a'+'A';
  putchar(ch);
  ch=getchar( );
}