Single Linked List Using C

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

typedef struct Node
{
    int data;
    struct Node *next;
}node;

node *HEAD=NULL;

//Interface Functions
int insert(int value);
int insert_at(int value,int position);
int remove_at(int position);
int search(int value);
void display();

//Internal Functions
node *new_node(int data,node* link);
void get_input(char str[],int* param);
void respond(char name[],int flag);
int length();

void main()
{
    int choice,value,position,flag=0;

    while(1)
    {
        printf("\t\tSINGLE LINKED LIST OPERATIONS\n");
        printf("1.Insert | 2.Insert at | 3.Remove at | 4.Search | 5.Display | 6.Exit\n");

        get_input("Choice",&choice);

        switch(choice)
        {
            case 1:
                    get_input("Value",&value);
                    flag=insert(value);
                    respond("Insertion",flag);
                    break;
            case 2:
                    get_input("Value",&value);
                    get_input("Position",&position);
                    flag=insert_at(value,position);
                    respond("Insertion",flag);
                    break;
            case 3:
                    get_input("Position",&position);
                    flag=remove_at(position);
                    respond("Deletion",flag);
                    break;
            case 4:
                    get_input("Value",&value);
                    if (search(value))
                    printf("Element is at position %d.\n\n",search(value));
                    else
                    printf("Element not found.\n\n");
                    break;
            case 5:
                    display();
                    break;
            case 6:
                    exit(0);
            default:
                    printf("Invalid Choice. Try Again.\n\n");
        }
    }
}

//Internal Functions
node *new_node(int value,node *link)
{
    node *temp=(node *)malloc(sizeof(node));
    if(temp==NULL)
    {
        printf("Memory allocation failure.\n\n");
        exit(0);
    }
    temp->data=value;
    temp->next=link;
    return temp;
}

void get_input(char str[],int *param)
{
    printf("Enter %s: ",str);
    scanf("%d",param);
}

void respond(char operation[],int flag)
{   
    if(flag)
    printf("%s Successful.\n\n",operation);
    else
    printf("%s not Successful.\n\n",operation);
}

int length()
{
    int size;
    node *temp=HEAD;
    if(HEAD==NULL)
    return 0;
    for(size=1;temp->next!=NULL;size++)
    temp=temp->next;
    return size;
}

//Interface Functions
int insert(int value)
{
    node *new=new_node(value,NULL);
    node *temp=HEAD;

    if (HEAD==NULL)
    {
        HEAD=new;
        return 1;
    }
    else
    {
        while(temp->next!=NULL)
        temp=temp->next;

        temp->next=new;
        return 1;
    }
    return 0;
}

int insert_at(int value,int position)
{
    node *new=new_node(value,NULL);
    node *temp=HEAD;


    if (position>length())
    {
        if (length()==0)
        {
            printf("List is empty.\n");
            return 0;
        }
        printf("Position is farther than size of list.\n");
        return 0;
    }

    if (position==1)
    {
        if(HEAD==NULL)
        {
            HEAD=new;
            return 1;
        }

        new->next=HEAD;
        HEAD=new;
        return 1;
    }

    if(position<=length())
    {
        for(int i=1;i<position-1;i++)
        temp=temp->next;

        new->next=temp->next;
        temp->next=new;
        return 1;
    }

    return 0;
}

int remove_at(int position)
{
    node *temp=HEAD;
    node *del;

    if (position<=0)
    {
        printf("Invalid Position.\n");
        return 0;
    }

    if (position>length())
    {
        if (length()==0)
        {
            printf("List is empty.\n");
            return 0;
        }
        printf("Position is farther than size of list.\n");
        return 0;
    }

    if (position==1)
    {
        HEAD=HEAD->next;
        free(temp);
        return 1;
    }

    if (position<=length())
    {
        for(int i=1;i<position-1;i++)
        temp=temp->next;

        del=temp->next;
        if (position==length())
        temp->next=NULL;
        else
        temp->next=del->next;
        free(del);
        return 1;
    }

    return 0;
}

int search(int value)
{
    node *temp=HEAD;
    int pos;

    if (HEAD==NULL)
    {
        printf("List is empty.\n");
        return 0;
    }

    for(pos=1;pos<=length();pos++,temp=temp->next)
    if(temp->data==value)
    return pos;

    return 0;
}

void display()
{
    node *temp=HEAD;

    if(HEAD==NULL)
    {
        printf("List is Empty.\n\n");
        return;
    }

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

    return;
}