指针有关问题，求！

指针问题，急求！！
在已经存储好数据的指针，要怎样改变它所指向的的值并且能将改正好的指针，能够很好的体现在一个链表里，其实就是链表里数据的修改要怎样完成，下面是我写的代码，错误可能会很多，多次修改还是不知道要怎样修改
主要就是红色的代码：
void changedata(linklist *L)
{
    linklist *pt1, *pt2;
char str_num[20];
if(L->next==NULL)
    {
        printf("无需修改，该表为空表\n");
    }
    else
    {
printf("请输入您要修改的编号信息:");
scanf("%s",str_num);
pt1=L->next;
pt2=(linklist*)malloc(sizeof(linklist));
while(pt1!=NULL)
    {
if(strcmp(pt1->num,str_num)==0)
{
    printf("\n输入添加货物的信息：");
    printf("\n请输入货物编号：");
            scanf("%s",&pt2->num);
            printf("\n请输入货物名称：");
            scanf("%s",&pt2->name);
            printf("\n请输入货物进货价：");
            scanf("%f",&pt2->purchase);
            printf("\n请输入货物销售价：");
            scanf("%f",&pt2->sales);
            printf("\n请输入货物生产日期：");
            scanf("%s",pt2->MFG);
            printf("\n请输入货物和保质期：");
            scanf("%s",pt2->EXP);
            printf("\n请输入货物库存量；");
            scanf("%d",&pt2->VMI);
            printf("\n请输入货物销售数量；");
            scanf("%d",&pt2->SV);
            pt1=&pt2;
    pt2->next=pt1->next;
}
pt1=pt1->next;  }
    }
}
------解决方案--------------------

void changedata(linklist *L)

 {

     linklist *pt1, *pt2;

     char str_num[20];

     if(L->next==NULL)

     {

         printf("无需修改，该表为空表\n");

     }

     else

     {

        printf("请输入您要修改的编号信息:");

        scanf("%s",str_num);

        pt1=L->next;

  //      pt2=(linklist*)malloc(sizeof(linklist));

        while(pt1 != NULL)

        {

            if(strcmp(pt1->num,str_num)==0)

            {

                printf("\n输入添加货物的信息：");

                printf("\n请输入货物编号：");

                fscanf(STDIN, "%s", pt1->num);

                printf("\n请输入货物名称：");

                fscanf(STDIN, "%s", pt1->name);

                printf("\n请输入货物进货价：");

                fscanf(STDIN, "%f", &pt1->purchase);

                printf("\n请输入货物销售价：");

                fscanf(STDIN, "%f", &pt1->sales);

                printf("\n请输入货物生产日期：");

                fscanf(STDIN, "%s", pt1->MFG);

                printf("\n请输入货物和保质期：");

                fscanf(STDIN, "%s", pt1->EXP);

                printf("\n请输入货物库存量；");