Stack implementation using Linked List in c

linked_stack.c

#include <stdio.h>
#include<stdlib.h>
struct node
{
    int val;
    struct node *link;
};

struct node* getnode( )
{
    return ( struct node *)malloc( sizeof( struct node ));
};
int c=0,n;
struct node* push( struct node *); struct node* pop( struct node *);
void display( struct node *);
struct node* top;
int main()
{
  struct node *F;
  int ch;
  printf("Enter the size in stack: ");
  scanf("%d",&n);
  F = NULL;
  while( 1 )
  {
      printf("1. To push\n");
      printf("2. To pop\n");
      printf("3. Display \n"); printf("4. Exit\n");
      scanf("%d", &ch );
      if( ch == 1 )
        F = push (F);
      else if( ch == 2 )
       F = pop (F);
      else if( ch == 3 )
        display(F);
      else
        break;
  }
}

struct node* push( struct node *FIRST)
{   if(c==n)
  {
    printf("Over-flow\n"); return(FIRST);
  }
    struct node *T;
    if( FIRST == NULL )
    {
        FIRST = getnode();
        T =top=FIRST;
    }
    else
    {
        T = FIRST;
        while( T->link != NULL ) T = T->link;

        T->link = getnode( );
        T = T->link;  top=T;
    }
    printf("Enter the element to push\n"); c++;
    scanf("%d", &T->val);
    T->link = NULL;
    return FIRST;
}
struct node* pop( struct node *FIRST)
{ struct node* T;
  struct node* P; P=FIRST;
    if(FIRST==NULL)
    {printf("stack-underflow\n"); return FIRST;}
    T=top;
    printf("The poppped out value is: %d\n",T->val);
    while(P->link!=NULL)
    { T=P;
      P=P->link;
    }
    top=T; top->link=NULL; c--;
    if(c==0)
    FIRST=NULL;
    return FIRST;
}
void display( struct node *T)
{   if(c==0)
    {
        printf("The stack is empty.\n"); return;
    }
    printf("The stack contains :  \n");
    while( T!= NULL )
    {
        printf("%d  ",T->val);
        T = T->link;
    }
    printf("\n");
}