//program for stack using array

#include<stdio.h>

void push();

void pop();

void peep();

void update();

int main()

{

int n,a[100],top=0;

//function for pushing the element

void push()

{

printf("\nenter the value to insert");

scanf("%d",&n);

top=top+1;

a[top]=n;

}

//function for poping the element out

void pop()

{

if(top==0)

{

printf("\nstack is empty");

}

else

{

int item;

item=a[top];

top=top-1;

printf("\npoped item is %d ",item);

}

}

//function for peeping the element from top of the stack

void peep()

{

int i;

printf("\nenter the element position to view from top");

scanf("%d",&i);

if(top-i+1<0)

{

printf("\nunderflow condition");

}

else

{

int x;

x=a[top-i+1];

printf("\nthe %dth element from top is %d",i,x);

}

}

//function to update the element of stack

void update()

{

int i,n;

printf("\nenter the position to update");

scanf("%d",&i);

printf("\nenter the item to insert");

scanf("%d",&n);

if(top-i+1<0)

{

printf("\nunderflow condition");

}

else

{

a[top-i+1]=n;

}

}

int x;

while(1)

{

printf("\n1.push");

printf("\n2.pop");

printf("\n3.peep");

printf("\n4.update");

printf("\nenter your choice");

scanf("%d",&x);

switch(x)

{

case 1:

push();

break;

case 2:

pop();

break;

case 3:

peep();

break;

case 4:

update();

break;

default:

printf("\ninvalid choice");

}

}

return(0);

}