Insert a Node Between The Single link list program in C using switch-Studyinight Programmer

#include<stdio.h>
#include<stdlib.h>
void insert();
void display();
int length();
struct node
{
    int data;
    struct node* next;
};
root=NULL;
void insert()
{
    int loc;
    struct node* temp;
    temp=(struct node*)malloc(sizeof(struct node));
    printf("Enter Data\n");
    scanf("%d",&temp->data);
    temp->next=NULL;
    struct node* p;
    p=root;
printf("Enter location where you want to insert node \n");
scanf("%d",&loc);
if(root==NULL)
    root=temp;
else if(loc>length())
    printf("insertion not possible\n");
    else if(loc==1)
    {
        temp->next=root;
        root=temp;
    }
else
{
    int i;
    for(i=1;i<loc-1;i++)
    {
        p=p->next;
    }
    temp->next=p->next;
    p->next=temp;
}
}
int length()
{
struct node *p;
p=root;
int count =0;
while(p!=NULL)
{
    count++;
    p=p->next;
}
return count;
}
void display()
{
  struct node * temp;
  temp=root;
  if(temp==NULL)
        printf("List is Empty\n");
  else
  {
      while(temp!=NULL)
      {
          printf("%d-->",temp->data);
          temp=temp->next;
      }
      printf("NULL\n");
  }
}
int main()
{
    int ch,len;
    while(1)
    {
        printf("1.Insert element between the Link list\n");
        printf("2.Length of the list\n");
        printf("3.Display element\n");
        printf("4.exit\n");
        printf("Enter your choice\n");
        scanf("%d",&ch);
        switch(ch)
        {
        case 1:
            insert();
            break;
        case 3:
            display();
            break;
        case 4:
            exit(1);
        case 2:
            len =length();
            printf("%d\n",len);
    break;
        default:
            printf("Please enter right choice\n");
        }
    }
}