#include
int main(){
char a,b;
printf("Please input a letter.\n");
scanf("%c",&a);
while(a<=64||(a>=91&&a<=96)||a>=123){
printf("Input error! please input a letter again.\n"); //为何打印了两次呀T.T
scanf("%c",&a);
}
/*
if(a>64&&a
printf("%c",a);
}
if(a>96&&a<123){
b=a-32;
printf("%c",b);
}
*/
(a<91)?(printf("%c",a)):(printf("%c",a-32));
}