Stack implementation using Array - c program (stack operation)

Stack implementation using Array - c program (stack operation)
===================================================

#include <stdio.h>
#include <conio.h>
#define size 10

int top = -1;
int stack[size];
int flag = 0;

void push (int *,int);
int pop (int *);
int peep (int *,int);
int update (int *,int);
void display (int *);

void main ()
{
int info,popped_element,position,data,pos_update,update_element,update_data;
char ch;

clrscr ();

do
{
printf("\n\ni<-Insert(push), d<-Delete(pop),p<-peep,u<-update, q<-Quit\n");
fflush (stdin);
printf("\n\nEnter your choice: ");
scanf("%c",&ch);
switch (ch)
{
case 'i':
{
printf("\n\nEnter the element you want to push: ");
scanf("%d",&info);
push (stack,info);
display (stack);
break;
}

case 'd':
{
popped_element = pop(stack);

if (flag == 0)
printf("\n\nThe element popped is %d",popped_element);
if (flag == 1)
printf("\nStack Underflow");
display (stack);
break;
}

case 'p':
{
printf("\n\nEnter the position of the stack from which you want to peep the element: ");
scanf("%d",&position);
data = peep(stack,position);
if (flag == 1)
printf("\nInvalid choice\n");
else
printf("The element peeped is %d",data);
display (stack);
break;
}

case 'u':
{
printf("Enter the position of the stack from which you want to update the data: ");
scanf("%d",&pos_update);
update_element = update(stack,pos_update);
if (flag == 1)
printf("Data can't be updated due to some reason");
else
printf("The data updated is %d",update_element);
display (stack);
break;
}

case 'q':
exit(0);
}
}while (ch != 'q');

getch ();
}

void push (int stack[],int info)
{
if (top == size-1)
printf("\nStack Overflow");
else
{
top++;
stack[top] = info;
}
}

int pop (int stack[])
{
int popped_element;
if (top == -1)
flag = 1;
else
{
flag = 0;
popped_element = stack[top];
top--;
}
return (popped_element);
}

void display (int stack[])
{
int i;
printf("\n\nThe contents of the stack are:\n");
for (i = top ; i >= 0 ; i--)
printf("%d ",stack[i]);
}

int peep (int stack[],int i)
{
int data;
if (top - i + 1 < 0)
flag = 1;
else
{
flag = 0;
data = stack[top-i+1];
}
return (data);
}

int update(int stack[],int pos)
{
int old_data;
if (top - pos + 1 < 0)
flag = 1;
else
{
flag = 0;
old_data = stack[top-pos+1];
printf("Enter the data you want to insert: ");
scanf("%d",&stack[top-pos+1]);
}
return (old_data);
}


Stack implementation using link list - c program
==============================

#include <stdio.h>
#include <conio.h>
struct Stack
{
int info;
struct Stack *next;
};
typedef struct Stack node;
node *first = NULL;
node *push (node *);
node *pop (node *);
void display (node *);

void main ()
{
char ch;

clrscr ();

do
{
fflush (stdin);
printf("\n\ni<-insert(push), d<-delete(pop), q<-quit\n");
printf("\n\nEnter the choice: ");
scanf("%c",&ch);
switch (ch)
{
case 'i':
{
first = push (first);
printf("\n\nAfter the push operation the stack is as follows:\n");
display (first);
break;
}

case 'd':
{
first = pop (first);
printf("\n\nAfter the pop operation the stack is as follows:\n");
display (first);
break;
}

case 'q':
exit (0);
}
}while (ch != 'q');

getch ();
}

node *push(node *first)
{
node *data;
data = (node *)malloc(sizeof(node));
printf("\nEnter the data to be inserted: ");
scanf("%d",&data->info);
data->next = first;
first = data;
return (first);
}

node *pop (node *first)
{
node *temp;
if (first == NULL)
printf("\n\nSTACK IS EMPTY\n");
else
{
temp = (node *)malloc(sizeof(node));
temp = first;
first = first->next;
printf("\nThe element deleted is %d",temp->info);
free (temp);
}
return (first);
}

void display (node *first)
{
while (first != NULL)
{
printf("%d ",first->info);
first = first->next;
}
}