程序执行到findList就自动退出了

#include<stdio.h>
#include <malloc.h>
#include <string.h>
typedef struct Node
{
    char instruct[10];
    long int num;    //学号
    char name[20];  //姓名
    char sex[2];    //性别
    double chinese; //语文
    double math;    //数学
    double english; //英语
    struct Node* next;
} PolyNode;

void insertTail(PolyNode* L, long int num , char *name , char sex, double chinese, double math, double english) {
    PolyNode* p = L->next;
    PolyNode* s,* pre = L;
    s = (PolyNode*)malloc(sizeof(PolyNode));
    while (p != NULL) {
        pre = p;
        p = p->next;
    }
    s->num = num;
    strcpy(s->name,name);
    s->sex[0] = sex;
    s->chinese = chinese;
    s->math = math;
    s->english = english;

    s->next = pre->next;
    pre->next = s;
}

PolyNode* createList() {
    PolyNode* L;
    L = (PolyNode*)malloc(sizeof(PolyNode));
    L->next = NULL;
    return L;
}

void printList(PolyNode* L) {
    PolyNode* p = L->next;
    while (p != NULL) {
        printf("0%d %s %c %.1lf %.1lf %.1lf\n", p->num,p->name, p->sex[0], p->chinese, p->math, p->english);
        p = p->next;
    }
}

void findList(PolyNode* L,long int num) {
    PolyNode* p = L->next,* pre = L;
    while (p->num != num && p != NULL) {
        pre = p;
        p = p->next;
    }
    if (pre->num == num) {
        printf("0%d %s %c %.1lf %.1lf %.1lf\n", pre->num, pre->name, pre->sex[0], pre->chinese, pre->math, pre->english);
    }  
    else {
        printf("Failed\n");
    }
}

int main() {
    char a[10],name[20],sex[2];
    long int num;
    double chinese, math, english;
    PolyNode* L = createList();
    PolyNode* head = L;
    while (1) {
        scanf("%s", a);
        if (a[0] == 'I') {
            scanf("%d %s %c %lf %lf %lf", &num, name, &sex[0], &chinese, &math, &english);
            insertTail(L,num,name,sex[0], chinese, math, english);
            printf("Insert:\n");
            printList(L);
            L = L->next;
        }
        if (a[0] == 'Q' || a[0] == 'E') {
            printf("Good bye!\n");
            break;
        }
        if (a[0] == 'L') {
            printf("List:\n");
            printList(head);
        }
        if (a[0] == 'F') {
            scanf("%d", &num);
            printf("Find:");
            findList(head,num);
        }
    }
}

你调试一下，看看因为什么原因退出，当时相关变量的值是多少