c语言返回值为3221225725

写了一个动态链表的建立和删除函数，执行删除函数只能删除有的元素，删除没有的元素，希望程序打印“没有找到节点”，但是一输入数据就返回3221225725
代码如下

#include<stdio.h>
#include<malloc.h>

struct Student {
    int   num;
    int   score;
    struct Student* next;
};
 
int n;
struct Student* a()
{
    struct Student* head, * p1, * p2;
    n = 0;
    p1 = p2 = (struct Student*)malloc(sizeof(struct Student));
    printf("请输入第%d位的成绩:",n+1);
    scanf("%d%d", &p1->num, &p1->score);
    head = NULL;
    while (p1->num != 0)
    {
        n = n + 1;
        if (n == 1)
        {
            head = p1;
        }
        else
        {
            p2->next = p1;
            p2 = p1;
        }
        p1 = (struct Student*)malloc(sizeof(struct Student));
        printf("请输入第%d位的成绩:", n + 1);
        scanf("%d%d", &p1->num, &p1->score);        
        p2->next = NULL;
    }
    
    return head;
}
 struct Student* b(struct Student* head)
 {
     int b;
     struct Student * p1, *p2;
    p1=head;
    p2=NULL;

     printf("请输入删除的学生学号；");
     scanf("%d",&b);
    
     
         while(p1->num != b&&p1!=NULL)
     {
        p2=p1;
         p1=p1->next;
     }     
     if(p1==NULL)
       {
           printf("找不到节点\n");
        }    
         else
         {
             if(p1==head)
             {
                 head=p1->next;
             }
             else
             {
                 
                 p2->next=p1->next;
             }
             free(p1);
           }  
           return(head);
 }
int main()
{
    struct Student* pt;
    pt = a();
   pt=b(pt);
    while (pt)
    {
        printf("%d %d\n", pt->num, pt->score);
        pt = pt->next;
    }
    
    return 0;
}

程序执行

}

while(p1->num != b&&p1!=NULL)

• 以上这句话是有问题的，p1!=NULL这句话要放在前面判断，不然p1等于NULL的时候就会导致空指针访问了。

while(p1!=NULL&&p1->num != b)

应该先判断p1 != NULL在访问p1->num != b，否则p1==NULL的时候，对NULL调用num直接炸了

#include <stdio.h>
#include <malloc.h>
struct Student
{
    int num;
    int score;
    struct Student *next;
};
int n;
struct Student *a()
{
    struct Student *head, *p1, *p2;
    n = 0;
    p1 = p2 = (struct Student *)malloc(sizeof(struct Student));
    printf("请输入第%d位的成绩:", n + 1);
    scanf("%d%d", &p1->num, &p1->score);
    head = NULL;
    while (p1->num != 0)
    {
        n = n + 1;
        if (n == 1)
        {
            head = p1;
        }
        else
        {
            p2->next = p1;
            p2 = p1;
        }
        p1 = (struct Student *)malloc(sizeof(struct Student));
        printf("请输入第%d位的成绩:", n + 1);
        scanf("%d%d", &p1->num, &p1->score);
        p2->next = NULL;
    }
    return head;
}
struct Student *b(struct Student *head)
{
    int b;
    int flag = 1;
    struct Student *p2;
    p2 = (struct Student *)malloc(sizeof(struct Student));
    p2->next = head;
    printf("请输入删除的学生学号；");
    scanf("%d", &b);

    while (p2->next != NULL)
    {
        if (p2->next->num == b)
        {
            p2->next = p2->next->next;
            flag = 0;
            break;
        }
        p2 = p2->next;
    }
    if (flag)
    {
        printf("找不到节点\n");
    }

    return (p2->next);
}
int main()
{
    struct Student *pt;
    pt = a();
    pt = b(pt);
    while (pt)
    {
        printf("%d %d\n", pt->num, pt->score);
        pt = pt->next;
    }
    return 0;
}