Refactor Doubly Linked List implementation

DoublyLL.c

@@ -1,147 +1,131 @@
-
 #include <stdio.h>
 #include <stdlib.h>
 
-// Define the DLL Node
-struct Node {
-  int data;
-  struct Node *prev; // Pointer to previous node
-  struct Node *next; // Pointer to next node
-};
+/* Node structure */
+typedef struct node {
+    int data;
+    struct node *prev;
+    struct node *next;
+} NODE;
 
-// Global Head Pointer
-struct Node *head = NULL;
+/* Global head pointer */
+NODE *head = NULL;
 
-// a) Insert a node (Create/Append) - 15 Marks
-// We insert at the END to simulate "Creating" a list naturally
+/* Insert node at end (Create list) */
 void insert(int value) {
-  struct Node *temp;
+    NODE *newNode, *temp;
 
-  // 1. Allocate memory
-  struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
-  if (newNode == NULL) {
-    printf("Memory allocation failed\n");
-    return;
-  }
+    newNode = (NODE *)malloc(sizeof(NODE));
+    if (!newNode) {
+        printf("Memory allocation failed\n");
+        return;
+    }
 
-  // 2. Set data
-  newNode->data = value;
-  newNode->next = NULL; // Since it will be the last node
+    newNode->data = value;
+    newNode->next = NULL;
 
-  // 3. Case 1: List is Empty
-  if (head == NULL) {
-    newNode->prev = NULL; // First node has no prev
-    head = newNode;
-    printf("Node %d inserted as head.\n", value);
-    return;
-  }
+    if (head == NULL) {
+        newNode->prev = NULL;
+        head = newNode;
+        printf("Inserted %d\n", value);
+        return;
+    }
 
-  // 4. Case 2: List has data. Traverse to the end.
-  temp = head;
-  while (temp->next != NULL) {
-    temp = temp->next;
-  }
+    temp = head;
+    while (temp->next != NULL) {
+        temp = temp->next;
+    }
 
-  // 5. Link the new node
-  temp->next = newNode; // Old last node points to new node
-  newNode->prev = temp; // New node points back to old last node
+    temp->next = newNode;
+    newNode->prev = temp;
 
-  printf("Node %d inserted at end.\n", value);
+    printf("Inserted %d\n", value);
 }
 
-// b) Delete a node (by value) - 15 Marks
-void delete(int value) {
-  struct Node *temp = head;
+/* Delete node by value */
+void delete_value(int value) {
+    NODE *temp = head;
 
-  // 1. Check if list is empty
-  if (head == NULL) {
-    printf("List is empty.\n");
-    return;
-  }
-
-  // 2. Search for the node
-  while (temp != NULL && temp->data != value) {
-    temp = temp->next;
-  }
-
-  // 3. If node not found
-  if (temp == NULL) {
-    printf("Element %d not found.\n", value);
-    return;
-  }
-
-  // --- Deletion Logic ---
-
-  // Case A: Deleting the Head Node
-  if (temp == head) {
-    head = head->next; // Move head forward
-    if (head != NULL) {
-      head->prev = NULL; // New head's prev must be NULL
+    if (head == NULL) {
+        printf("List is empty\n");
+        return;
     }
-  }
-  // Case B: Deleting a Middle or Last Node
-  else {
-    // Link the previous node to the next node
-    temp->prev->next = temp->next;
 
-    // If there IS a next node (i.e., we are not deleting the last node),
-    // Link the next node back to the previous node
-    if (temp->next != NULL) {
-      temp->next->prev = temp->prev;
+    while (temp != NULL && temp->data != value) {
+        temp = temp->next;
     }
-  }
 
-  // 4. Free memory
-  free(temp);
-  printf("Node %d deleted.\n", value);
+    if (temp == NULL) {
+        printf("Element not found\n");
+        return;
+    }
+
+    if (temp == head) {
+        head = temp->next;
+        if (head != NULL)
+            head->prev = NULL;
+    } else {
+        temp->prev->next = temp->next;
+        if (temp->next != NULL)
+            temp->next->prev = temp->prev;
+    }
+
+    free(temp);
+    printf("Deleted %d\n", value);
 }
 
-// c) Display the list - 5 Marks
+/* Display list */
 void display() {
-  struct Node *temp = head;
+    NODE *temp = head;
 
-  if (head == NULL) {
-    printf("List is empty.\n");
-    return;
-  }
-
-  printf("List (Forward): NULL <-> ");
-  while (temp != NULL) {
-    printf("%d <-> ", temp->data);
-    temp = temp->next;
-  }
-  printf("NULL\n");
-}
-
-int main() {
-  int choice, val;
-  printf("--- Doubly Linked List Program ---\n");
-
-  while (1) {
-    printf("\n1. Insert (Create)\n2. Delete\n3. Display\n4. Exit\n");
-    printf("Enter choice: ");
-    scanf("%d", &choice);
-
-    switch (choice) {
-    case 1:
-      printf("Enter value: ");
-      scanf("%d", &val);
-      insert(val);
-      break;
-    case 2:
-      printf("Enter value to delete: ");
-      scanf("%d", &val);
-      delete(val);
-      break;
-    case 3:
-      display();
-      break;
-    case 4:
-      return 0;
-    default:
-      printf("Invalid Choice\n");
+    if (head == NULL) {
+        printf("List is empty\n");
+        return;
     }
-  }
-  return 0;
+
+    printf("List: ");
+    while (temp != NULL) {
+        printf("%d <-> ", temp->data);
+        temp = temp->next;
+    }
+    printf("NULL\n");
 }
 
+/* Main function */
+int main() {
+    int choice, value;
+
+    while (1) {
+        printf("\n--- DOUBLY LINKED LIST MENU ---\n");
+        printf("1. Insert\n");
+        printf("2. Delete\n");
+        printf("3. Display\n");
+        printf("4. Exit\n");
+        printf("Enter choice: ");
+        scanf("%d", &choice);
+
+        switch (choice) {
+        case 1:
+            printf("Enter value: ");
+            scanf("%d", &value);
+            insert(value);
+            break;
+
+        case 2:
+            printf("Enter value to delete: ");
+            scanf("%d", &value);
+            delete_value(value);
+            break;
+
+        case 3:
+            display();
+            break;
+
+        case 4:
+            exit(0);
+
+        default:
+            printf("Invalid choice\n");
+        }
+    }
+}