#include?<string.h>
void?main()
{
int?i,n;
char?ch[1000];
gets(ch);
n=strlen(ch);
for(i=0;i<n;i++)
if(ch[i]>='A'&&ch[i]<='Z')?ch[i]+=32;
else?if(ch[i]>='a'&&ch[i]<='z')?ch[i]-=32;
printf("%c",ch[i]);
}
運行示例: