SELECT:
        getchar();//消除残余回车符
        printf("Again?(y/n)");
        switch(getchar())//这里可以用getch(),无回显
        {
            case 'n':
                exit(0);
            case 'y':
                break;
            default:
                printf("Unknown selectin!\n");
                goto SELECT;
        }
        fflush(stdin);

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