#include<stdio.h>

#include<stdlib.h>

int main(){

int ch = 0;

printf("輸入一個字元!\n");

while ((ch = getchar()) != 0){ //迴圈中ch均表示為ASCII值

if (ch >= "a"&&ch <= "z"){

printf("%c", ch - 32);

}

if (ch >= "A" && ch <= "Z"){

printf("%c", ch + 32);

}

if (ch >= "0"&&ch <= "9"){

printf("無效輸入!");

}

}

system("pause");

return 0;

}