Linked List implementation

LinkedList.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);
int length(void);
void reverse(void);
// Intializing
struct node{
  int data;
  struct node* link;
};

struct node* root = NULL;
int len;
//---------------------------------------------------------------------------------------------------
int main(){
    
    while(1){
        printf("\nSingle 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");
            
        }
        
    }

    return 0;
}
//---------------------------------------------------------------------------------
void append(){
    
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));
    printf("\nEnter node data : ");
    scanf("%d", &temp -> data);
    temp -> link = NULL;
    
    if (root == NULL){
        root = temp;
    }
    else{
        struct node * p;
        p = root;
        while (p-> link != NULL ){
            p = p -> link;
        }
        
        p -> link = temp;
        
    }
}
//-------------------------------------------------------------------------------
int length(){
    struct node* temp;
    int count = 0 ;
    temp = root;
    
    while(temp != NULL){
        temp = temp -> link;
        count ++;
    }
    
    len = count;
    if (count == 0){
        printf("\nList is empty\n");
        
    }
    else {
        printf("\nTotal number of elements in list : %d\n",len);
    }
    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 -> link;
        }
        printf("NULL");
    }
    printf("\n");
    
}
//----------------------------------------------------------------------------------------------------
void add_begin(){
    
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));
    printf("Enter node data : ");
    scanf("%d", &temp -> data);
    temp -> link = root;
    root = temp;
    
}
//------------------------------------------------------------------------------------------------------
void add_after(){
    
    printf("\nEnter the element after which you want to insert : ");
    int loc;
    scanf("%d",&loc);
    
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));
    printf("\nEnter node data : ");
    scanf("%d", &temp -> data);
    
    struct node* p;
    p = root;
    if (p == NULL){
        printf("\nThere is no node in list\n");
    }
    else{
        
        while (p -> link != NULL){
            if(p -> data == loc){
              break;
            }
            else{
              p = p->link ;
            }          
        }        
        if (p ->link == NULL && p -> data == loc){
            temp -> link = NULL;
            p -> link = temp;
        }
        else if (p -> link == NULL){
            printf("\nEntered element does not exist in list\n");
        }
        else{
            temp -> link = p -> link;
            p -> link = temp;
            
        }         
    }
}
//------------------------------------------------------------------------------------------------------
void delete_node(){
    struct node* p, *q ,*t;
    p = root;
    int count = 0;
    
    if (p != NULL){
        
        printf("\nEnter the element to delete : ");
        int loc;
        scanf("%d", &loc);
        while (p-> link != NULL ){
            
            if (p -> data == loc){
                break;
            }
            else{
                p = p -> link;
                if (count == 0){
                     t = p;
                }
                else if(count == 1){
                    q = p;
                }
                else {
                    t = q;
                    q = p;
                }
            }
            count ++;
        }
        
        if (count == 0){
            if (p-> link == NULL){
                root = NULL;
                p -> link = NULL;
                free(p);
            }
            else{
                root = p -> link;
                p -> link = NULL;
                free(p);
            }
        }
        
        else if (p -> link == NULL && p -> data == loc){
            
            t -> link = NULL;
            p -> link = NULL;
            free(p);
            
        }
        else if (p -> link == NULL){
            printf("\nEntered element is not in list.\n");
        }
        else{
            
            t -> link = p -> link;
            p -> link = NULL;
            free(p);
        }
    }
    else{
        printf("\nNothing to delete here.\n");
    }
}
//-------------------------------------------------------------------------
void reverse(){
  struct node* prev   = NULL;
    struct node* current;
    current = root;
    struct node* next;
    while (current != NULL)
    {
        next  = current->link;  
        current->link = prev;   
        prev = current;
        current = next;
    }
    if (prev != NULL){
      root = prev;
    }
}