任意字母大小写转换用C

#include"stdio.h"
main()
{
char ch;
printf("Please Input a number:\n");
ch=getchar();
while(ch!='\n')
{
if(ch>='a'&&ch<='z') putchar(ch-'a'+'A');
else if(ch>='A'&&ch<='Z') putchar(ch-'A'+'a');
else putchar(ch) ;
getchar();
printf("\nPlease Input a number:\n");
ch=getchar();
}
}