Stack

//Stack

#include<conio.h>
#include<stdio.h>
#define MAX 3

int st[MAX], top=-1;
//push (add)
void push(int st[], int val);
//pop (remove)
int pop(int st[]);
//peep (search)
int peep(int st[], int idx);
void display(int st[]);
void update(int st[], int val, int idx);

void main()
{
    int val, op, idx;
    clrscr();

    do
    {
        getch();
        clrscr();

        printf("\n Main Menu");
        printf("\n 1. Push");
        printf("\n 2. Pop");
        printf("\n 3. Peep");
        printf("\n 4. Display");
        printf("\n 5. Update");

        switch(op)
        {
            case 1:
            printf("Enter Number : ");
            scanf("%d", &val);
            push(st,val);
            break;

            case 2:
            val=pop(st);
            if(val==-1)
            {
                printf("\n The Value Deleted From The Stack");
            }
            break;

            case 3:
            printf("\n Enter The Index To Search : ");
            scanf("%d", &idx);
            if(idx<1)
            {
                printf("\n Invalid Index");
            }

            else
            {
                val=peep(st,idx);
                if(val != 1)
                {
                    printf("\n The Value Stored at Top Of The Stack is %d", val);
                }
            }
            break;

            case 4:
            printf("\n Enter The Number to Update on to The Stack : ");
            scanf("%d", &val);

            printf("\n Enter The Index To Be Update on The Stack : ");
            scanf("%d", &idx);

            if(idx<1)
            {
                printf("\n Invalid Index");
            }
            else
            {
                update(st, val, idx);
            }
            break;

            case 5:
            display(st);
            break;

        }
    }while (op!=6);
        getch();
}

void push(int st[], int val)
{
    if(top==MAX-1)
    {
        printf("\n Stack is Overflow");
    }
    else
    {
        top++;
        st[top]=val;
    }
}

int pop(int st[])
{
    int val;
    if(top==1)
    {
        printf("Stack is Underflow");
        return -1;
    }
    else
    {
        val=st[top];
        top--;
        return val;
    }
}

void display(int st[])
{
    int i;
    if(top == -1)
    {
        printf("\n Stack is Empty");
    }
    else
    {
        for(i=top;i>=0;i++)
        {
            printf("\n %d", st[i]);
        }
    }
}

int peep(int st[], int idx)
{
    if(top-idx+1<=-1)
    {
        printf("\n Stack is Underflow");
        return -1;
    }
    else
    {
        return(st[top-idx+1]);
    }
}

void update(int st[], int val, int idx)
{
    if(top-idx+1<=-1)
    {
        printf("\n Stack is Underflow");
    }
    else
    {
        st[top-idx+1]=val;
    }
}