//program for stack using array

#include <stdio.h>

void push();

void pop();

void peek();

void update();

int a[100], top = -1;

int main()

{

int x;

while (1)

{

printf("\n0.exit");

printf("\n1.push");

printf("\n2.pop");

printf("\n3.peek");

printf("\n4.update");

printf("\nenter your choice? ");

scanf("%d", &x);

switch (x)

{

case 0:

return 0;

case 1:

push();

break;

case 2:

pop();

break;

case 3:

peek();

break;

case 4:

update();

break;

default:

printf("\ninvalid choice");

}

}

return (0);

}

//function for pushing the element

void push()

{

int n = 0;

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

scanf("%d", &n);

top += 1;

a[top] = n;

}

//function for poping the element out

void pop()

{

if (top == -1)

{

printf("\nstack is empty");

}

else

{

int item;

item = a[top];

top -= 1;

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

}

}

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

void peek()

{

if (top >= 0)

printf("\n the top element is %d", a[top]);

else

printf("\nstack is empty");

}

//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;

}

}