使用递归在C中反向链表

Question

I have written following code in C. I am pretty new to C. The insert and Print functions seem to work fine but I get a prompt that says program stopped working when I call Reverse function. Where dis I go wrong ?

//WAP to reverse a Linked List using recursion

#include<stdio.h>
#include<stdlib.h>

struct Node{
    int data;
    struct Node* next;
};
struct Node* head;  //global variable

struct Node* Reverse(struct Node* p){
    if(p->next == NULL){  //since for last node link part is null
        head = p;
        printf("break condition");
        return head;
    }
    printf("calling reverse");
    Reverse(p->next);
    struct Node* q = p->next;
    q->next = p;
    p->next = NULL;
}

void Insert(int x){
    struct Node* temp= (struct Node*)malloc(sizeof(struct Node));
    temp->data = x;
    //temp->next = NULL; //redundant
    //if(head!= NULL){
    temp->next = head;  //temp.next will point to null when head is null nd otherwise what head was pointing to
    //}
    head = temp;
}

void Print(){
    struct Node* temp1 = head;  //we dont want tomodify head so store it in atemp. bariable and then traverse
    while(temp1 != NULL){
        printf(" %d", temp1->data);
        temp1= temp1->next;
    }
    printf("\n");
}

int main(){
    struct Node* head = NULL;
    Insert(2);
    Insert(4);
    Insert(5);
    Insert(1);
    Print();
    head = Reverse(head);
    //  Print();
}

Answer 1

There are two issues with the program above:

1) You have two head variables. One is a global variable, and the other is a variable local to the main function. That local variable is the one that is passed to Reverse() . Since the first thing that function does is dereferencing it, the program crashes. Removing the local head variable in the main() function should address it.

2) The Reverse() function correctly returns head when it reaches the exit condition, but what happens the rest of the time? It's missing a return in the non-exit condition case. Here's a diff that would address the issue:

    printf("calling reverse");
-   Reverse(p->next);
+   struct Node* ret;
+   ret = Reverse(p->next);
    struct Node* q = p->next;
    q->next = p;
    p->next = NULL;
+   return ret;