界面DisplayTeacherOPMenu显示正常,输入选项之后直接会退出,进不去循环怎么回事?

Question

int DisplayTeacherOPMenu()
{
    int ret = -1;
    char buf[4] = "";
    system("clear");
    printf("************学生信息管理系统*************\n");
    printf("*                    *\n");
    printf("*    您正在使用教师身份进行操作    *\n");
    printf("*                    *\n");
    printf("*    1.录入学生信息            *\n");
    printf("*    2.查看学生信息            *\n");
    printf("*    3.修改学生信息            *\n");
    printf("*    4.删除学生信息            *\n");
    printf("*    5.查看学生排名            *\n");
    printf("*    6.修改登录密码            *\n");
    printf("*    7.辞职                *\n");
    printf("*    0.注销                *\n");
    printf("*    please input:            *\n");
    printf("*                    *\n");
    printf("*****************************************\n");
    system("tput cup 12 21");
    MyGetString(buf, 4);
    sscanf(buf, "%d", &ret);
    return ret;
}

int TeacherLoop(struct StuHead* pstTea)
{
    struct StuHead* pstStuList = NULL;
    struct StuHead* pstStuHead = NULL;
    struct StuNode* pstStuNode = NULL;
    struct TeaNode* pstTeaNode = NULL;

    int cmd = -1;
    int exitflag = 0;
    int id;
    while (1) {
        pstStuHead = CreateStuListHead();
        ReadStuDataFromFile(pstStuHead);
        cmd = DisplayTeacherOPMenu();

        switch (cmd) {
        case 1:
            getStuData(pstStuHead);
            PrintAllStu(pstStuHead);
            break;
        case 2:
            system("clear");
            printf("请输入要查找的学生学号:");
            scanf("%d", &id);
            pstStuNode = SearchStuNodeByID(pstStuHead, id);
            if (pstStuNode == NULL) {
                printf("学生不存在!\n");
                break;
            }
            printf("Name:%s ID:%d Sex:%c C:%.1f Math:%.1f Chn:%.1f\n",
                pstStuNode->data.name, pstStuNode->data.id,
                pstStuNode->data.sex, pstStuNode->data.CScore,
                pstStuNode->data.MathScore, pstStuNode->data.ChnScore);
            break;
        case 3:
            //修改学生信息
            break;
        case 4:
            printf("请输入要删除的学生学号:\n");
            scanf("%d", &id);
            getchar();
            pstStuNode = SearchStuNodeByID(pstStuHead, id);
            RemoveStuNode(pstStuHead, pstStuNode);
            // SaveStuDataToFile(pstStuHead);
            break;
        case 5:
            StuSortMenu(pstStuList);
            break;
        case 6:
            ChangeTeaPassword(pstTeaNode);
            break;
        case 7:
            //辞职
            break;
        case 0:
            exitflag = 1;
            break;
        }
        if (exitflag) {
            break;
        }
    }
    return 0;
}