大小写字母转换

#include<stdio.h>
int main(){
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();
}
return 0;
}