Stack using Linked List in C

#include<stdio.h>
#include<conio.h>
#include<malloc.h>
struct stack
{
int no;
struct stack *next;
};
typedef struct stack stc;
void add();
void del();
void display();
stc *top=NULL,*ptr=NULL;

void main()
{
int ch;
char choice;
clrscr();
do
{
printf("\t\t\t Stack As Linked List\n");
printf("1.Add\n");
printf("2.Delete\n");
printf("3.Display\n");
printf("4.Exit\n");
printf("Enter your choice..:");
scanf("%d",&ch);

switch(ch)
{
case 1:
add();
break;
case 2:
del();
break;
case 3:
display();
break;
case 4:
exit();
default:
printf("Sorry Wrong Choice...!");
}
printf("Do you want to continue-->");
fflush(stdin);
scanf("%c",&choice);
}while(choice=='y'||choice=='Y');
}
void add()
{
if(top==NULL)
{
top=(stc *)malloc(sizeof(stc));
ptr=top;
top->next=NULL;

}
else
{
top->next=(stc *)malloc(sizeof(stc));
top->next=NULL;
top=top->next;
}
printf("Enter value to add-->");
scanf("%d",&top->no);
printf("Value of ptr : %d",ptr->no);
}
void del()
{
stc *temp,*ptr1;
ptr1=ptr;
if(top->next==NULL && ptr1->next==NULL)
{
temp=top;
top=NULL;
ptr1=NULL;
printf("Deleted value : %d",temp->no);
free(temp);
ptr=NULL;

}
else
{
while(ptr1->next->next!=NULL)
{
ptr1=ptr1->next;
}
temp=top;
top=ptr1;
top->next=NULL;

printf("Deleted value=%d",temp->no);
free(temp);
}
}
void display()
{
printf("\n\nDisplay\n");
while(ptr!=NULL)
{
printf("\n%d",ptr->no);
ptr=ptr->next;
}
}

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