Implementation of stack in C

#include<iostream.h>

#include<conio.h>

#include<stdio.h>

#include<process.h>

int top=-1;

int *stk;

void PUSH(int n)

{    if(top>n)

    cout<<"\nSTACK OVERFLOW";

    else

    {       top++;

        cout<<"\nEnter the element to be inserted:";

        cin>>stk[top];

    }

}

void POP()

{       if(top<0)

    cout<<"\nSTACK UNDERFLOW";

    else

    { int item=stk[top];

        top--;

        cout<<"\nThe deleted element is:"<<item;

    }

}

void PEEP()

{       int pos;

    cout<<"\nEnter the element position u want to search:";

    cin>>pos;

    if(top-pos+1<=0)

    cout<<"\nSTACK UNDERFLOW";

    else

    {    cout<<"\nRequired element:"<<stk[top-pos+1];

    }

}

void TRAVERSE()

{       int pos,value;

 /*    cout<<"\nEnter the position u want to change value:";

    cin>>pos;

    cout<<"\nEnter the value to be change:";

    cin>>value;

    if(top-pos+1<=0)

    cout<<"\nSTACK UNDERFLOW";

    else

    {    stk[top-pos+1]=value;

    }*/

}

void main()

{    clrscr();

    int n,i;

cout<<"\nEnter the size of stack:\n";

    cin>>n;

    again:

    cout<<"Enter your choice:";

    cout<<"1.PUSH\n";

    cout<<"2.POP\n";

    cout<<"3.PEEP\n";

    cout<<"4.CHANGE\n";

    cin>>i;

    switch(i)

    {

        case 1:PUSH(n);

            break;

        case 2:POP();

            break;

        case 3:PEEP();

            break;

        case 4:CHANGE();

            break;

        default:exit(0);

    }

    cout<<"  Do u want to continue(Y=1/N=0):";

        int x;

        cin>>x;

        if(x==1)

        {

        goto again;

         }

         else

         {

         exit(0); }

    getch();

}

/* output:-

Enter the size of stack:

3

Enter your choice:1.PUSH

2.POP

3.PEEP

4.CHANGE

1

Enter the element to be inserted:4

  Do u want to continue(Y=1/N=0):1

Enter your choice:1.PUSH

2.POP

3.PEEP

4.CHANGE

1

Enter the element to be inserted:5

  Do u want to continue(Y=1/N=0):1

Enter your choice:1.PUSH

2.POP

3.PEEP

4.CHANGE

1

Enter the element to be inserted:6

  Do u want to continue(Y=1/N=0):1

Enter your choice:1.PUSH

2.POP

3.PEEP

4.CHANGE

4

Enter the position u want to change value:2

Enter the value to be change:55

  Do u want to continue(Y=1/N=0):1

Enter your choice:1.PUSH

2.POP

3.PEEP

4.CHANGE

3

Enter the element position u want to search:2

Required element:55  Do u want to continue(Y=1/N=0):

0

*/