Doubly Linked List implementation

DoublyLinkedList.c

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

//Prototyping 
void append(void);
void add_begin(void);
void add_after(void);
void delete_node(void);
void display(void);
void reverse(void);
int length(void);

// Intializing
struct node{
  struct node* prev;
  int data;
  struct node* next;
};

struct node* root = NULL, *end = NULL;
int len;

//---------------------------------------------------------------------------------------------------
int main(){
    
    while(1){
        printf("\nDoubly liked list operations : \n");
        int option;
        printf(" 1. Append \n 2. Add at begin \n 3. Add at after \n 4. Length \n 5. Display \n 6. Delete \n 7. Reverse \n 8. Quit \n");
        printf("Enter your choice : ");
        scanf("%d", &option);
        
        switch(option){
            
            case 1 : append();
                     break;
                     
            case 2 : add_begin();
                     break;
                     
            case 3 : add_after();
                     break;
                     
            case 4 : length();
                     break;
                     
            case 5 : display();
                     break;
                     
            case 6 : delete_node();
                     break;

            case 7 : reverse();
                     break;

            case 8:  exit(0);
                     break;

            default : printf("\nInvalid Input \n");
            
        }    
           printf("%d", end -> data); 
    }
    return 0;
}

//---------------------------------------------------------------------------------
void append(){
  struct node* temp;
  temp = (struct node*)malloc(sizeof(struct node));
  printf("\nEnter node data : ");
  
  scanf("%d",&temp -> data);
  temp -> prev = NULL;
  temp -> next = NULL;

  if(root == NULL){
    root = temp;
    temp -> prev = root;
    end = temp;
  }
  else{
    struct node* p;
    p = root;

    while (p-> next != NULL){
      p = p -> next;      
    }

    p -> next = temp;
    temp -> prev = p;
    end = temp;
  }

}

//-------------------------------------------------------------------------------
int length(){
  struct node* p;
  p = root;
  int count = 0;
  
  while (p != NULL){
    p = p -> next;
    count++;
  } 

  len = count; 
  if (count == 0){
    printf("\nList Empty\n");
  }
  else{
    printf("\nTotal elements in list : %d\n",count);
    
  }
  return len;
}

//------------------------------------------------------------------------------------------
void display(){
    
   struct node* temp;
    temp = root;
    
    if( temp == NULL){
        printf("\nNothing to display\n");
    }
    else{
      printf("\n");

        while(temp != NULL){
            printf("%d --> ",temp -> data);
            temp = temp -> next;
        }

        printf("NULL");
    }
    printf("\n");
    
}

//----------------------------------------------------------------------------------------------------
void reverse(){
    
    struct node* temp;
    temp = end;    
    
    if( temp == NULL){
        printf("\nNothing to display\n");
    }
    else{
      printf("\nNULL");

        while(temp != root){
            printf("<--%d ",temp -> data);
            temp = temp -> prev;
        }

        printf("<--%d", root -> data);
    }
    printf("\n");
    
}

//----------------------------------------------------------------------------------------------------
void add_begin(){
  struct node* temp;
  temp = (struct node*)malloc(sizeof(struct node));  
  printf("\nEnter node data : ");
  scanf("%d",&temp->data);
  temp -> next = NULL;

  struct node* p;
  p = root;
  if (p == NULL){
    root = temp;
    temp -> prev = root;
    end = temp;
  }
  else{
    
    temp -> next = p;
    root = temp;
    temp -> prev = root;
    p -> prev = temp;
  }
    
}

//------------------------------------------------------------------------------------------------------
void add_after(){  

  if (root ==  NULL){
    
    printf("\nThere are no elements in the list\n");
    
  }
  else{

    int loc;
    printf("\nEnter element after which node to be inserted : ");
    scanf("%d", &loc);

    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));
    printf("\nEnter node data : ");
    scanf("%d",&temp->data);
    temp -> next = NULL;
    temp -> prev = NULL;   

    struct node* p;
    p = root;

    while(p->next != NULL ){
      if (p -> data == loc){        
        break;
      }
      else{
        p = p -> next;
      }
      
    }

    if (p-> next == NULL && p -> data != loc){
      printf("\nEntered element not found in the list\n");
    }

    else if (p -> next == NULL){
      p -> next = temp;
      temp -> prev = p;
      end = temp;
    }
    else{
      temp -> next = p -> next;
      p -> next = temp ;
      temp -> prev = p;
      
    }    
  }  
}
//------------------------------------------------------------------------------------------------------
void delete_node(){

  int loc;
  printf("\nEnter the element to be deleted : ");
  scanf("%d",&loc);

  struct node* p, *temp;
  p = root;

  if (root == NULL){
    printf("\nList empty\n");
  }
  else{
    int count =0;

    while(p -> next != NULL){
      if (p-> data == loc){
        break;
      }
      else{
        p = p -> next;
      }
      count ++;
    }

    if(count == 0){
      root = p -> next;
      p-> prev = NULL;
      free(p);
      end = NULL;
      
    }
    else{
      if (p -> next == NULL && p -> data != loc){
        printf("\nElement not found \n");
      }
      else if(p -> next == NULL){
        
        temp = p -> prev;
        temp -> next = NULL;        
        p -> prev = NULL;
        free(p);
        end = temp;        
        
      }
      else{
        struct node * temp;
        temp = p -> prev; 
        temp -> next = p-> next;       
        p -> prev = NULL;
        p -> next = NULL;
        free(p);
      }
    }
  }     
}