void change()
{
    int j,l,k;
    system("cls");  /*清屏*/
    for(j=0;j<m;j++)
    {    printf("%s   %d   %s   %s",stu[j].name,stu[j].num,stu[j].sex,stu[j].cla);
    printf("是否修改<y/Y>:\n");
    k=getche();
    if(k=='y')
    {printf("是否修改姓名<y/Y>:\n");
        k=getche();
        if(k=='y')
        {printf("请输入新的姓名:\n");
        scanf("%s",stu[j].name);}
        printf("是否修改学号<y/Y>:\n");
        k=getche();
        if(k=='y')
        {printf("请输入新的学号:\n");
        scanf("%d",&stu[j].num);}
        printf("是否修改性别<y/n>:\n");
        k=getche();
        if(k=='y')
        {printf("请输入新的性别:\n");
        scanf("%s",stu[j].cla);}
        printf("是否修改成绩<y/Y>");
        k=getche();
        if(k=='y');
        for(l=0;l<5;l++)
        {    printf("\n");
            printf("%d\n",stu[j].score[l]);
            printf("是否修改该科成绩<y/n>");
        k=getche();
        if(k=='y')
        {    printf("请输入该科修改后的成绩：");
        scanf("%d",stu[j].score[l]);}
        else continue;
        }
   
    }
    }
}

漏了&(取地址符)了!!!!

好滴吧~~~~~我经常把它忘了。。。。谢谢