linux - 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?

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;

}