C Program To Reverse Linked List

Example Program To Reverse Singly Linked List:

---

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

  struct sllNode {
        int data;
        struct sllNode *nextPtr;
  };

  struct sllNode *front = NULL;
  struct sllNode *rear = NULL;

  /*
    * creates Node and fill the given data
    */
  struct sllNode * createNode(int data) {
        struct sllNode *ptr = (struct sllNode *) malloc(sizeof (struct sllNode));
        ptr->data = data;
        ptr->nextPtr = NULL;
        return ptr;
  }

  /* inserting node at the end of the list */
  void insertionOp(int data) {
        struct sllNode *ptr =  createNode(data);
        if (rear == NULL) {
                front = ptr;
                rear = ptr;
        }
        rear->nextPtr = ptr;
        rear = ptr;
  }

  /* delete all nodes in the list */

  void deleteList() {

        struct sllNode *ptr;

        ptr = front;

        while (ptr){

                front = ptr->nextPtr;

                free(ptr);

                ptr = front;

        }

  }

  /* traverse the list and print the data in each node */

  int walkList() {

        struct sllNode *ptr;

        int i = 0;

        ptr = front;

        while (ptr) {

                printf("%d ", ptr->data);

                ptr = ptr->nextPtr;

                i++;

        }

        return (i);

  }

  /* reverse the linked list */

  void reverseList() {

        struct sllNode *xPtr, *yPtr, *zPtr;

        yPtr = zPtr = NULL;

        xPtr = front;

        while (xPtr) {

                zPtr = yPtr;

                yPtr = xPtr;

                xPtr = xPtr->nextPtr;

                yPtr->nextPtr = zPtr;

        }

        front = yPtr;

        return;

  }

  int main (int argc, char *argv[]) {

        int data, i, n;

        FILE *fp;

        fp = fopen(argv[1], "r");

        if (!fp) {

                printf("Unable to open the file\n");

                exit(0);

        }

        /* scan the inputs from the file & insert it into the list */

        while (fscanf(fp, "%d", &data) != EOF) {

                insertionOp(data);

        }

        printf("\nData in Linked List:\n");

        n = walkList();

        printf("\nNo of elements in linked list: %d\n", n);

        printf("\nData in Reversed Linked List:\n");

        reverseList();

        n = walkList();

        printf("\nNo of elements in linked list: %d\n\n", n);

        deleteList();

        return 0;

  }

Output: (C Program To Reverse Singly Linked List)

  6 5
  7 4
  8 2
 
  Data in Linked List:

  6 5 7 4 8 2 

  No of elements in linked list: 6

  Data in Reversed Linked List:

  2 8 4 7 5 6 

  No of elements in linked list: 6