#include <stdio.h>
#include <stdlib.h>

int main()
{
    char tuna = 'Q';
do{

    printf("%s\nDo you like tuna? y/n", (tuna!='Q') ? "Please enter a valid response." : "");
    scanf(" %s", tuna);

}while ((tuna!='y')||(tuna!='n'));
printf("%s", tuna);
}