[求助从键盘输入一个大写字母，要求改用小写字母输出..

main(){
char big;

printf("Input the up zimu:");
scanf("%c",&big);

while(big>'Z' || big <'A'){
printf("Error!Input the up zimu:");
scanf("%c",&big);
}

printf("%c\n",big-a+A);
}

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