#include <iostream>

using namespace std;

struct stack
{
 int *arr;     // The dynamic array to store the values
 int  size;    // How many positions the dynamic array current holds
 int  top;     // Indicating the number of values currently stored in the dynamic array
};

// set the stack so it can initially hold 10 values
// set the Top of the Stack to be zero (zero values currently stored on the stack)
void init ( stack & s )
{
 s.arr = new int[10];
 s.size = 10;
 s.top = 0;
}

// the value in top also tells how many values are currently
// stored on the stack
bool isEmpty ( stack s )
{
 if ( s.top == 0 )
   return true;
 else
   return false;
}

// return the value at the top-1st position
//   but first verify the stack is not empty
int top ( stack s )
{
 if ( isEmpty ( s ) == false )
   return ( s.arr[s.top-1] );   // note: the value of top does NOT change!
 else
   return -999;
}

// add a value to the stack
//   grow the array if needed
void push ( stack & s, int val)
{
 if ( s.top == s.size )
   { 
    // grow the array
    int *temp;
    temp = new int [s.size*2];
    for (int a = 0 ; a < s.size ; a++)
       temp[a] = s.arr[a];
    delete[] s.arr;
    s.arr = temp;
    s.size = s.size * 2;
   }

 s.arr[s.top] = val;
 s.top++;
}

// if the stack is not empty decrement the value of top
void pop ( stack & s )
{ 
 if ( isEmpty ( s ) == false )
   s.top--;
}

int main( )
{
 stack s1;

 init ( s1 );

 // add a single value to the stack
 push ( s1, 5 );

 cout << top ( s1 ) << endl ;

 // clear the stack
 while ( isEmpty ( s1 ) == false )
   {
     cout << top ( s1 ) << endl ;
     pop ( s1 );
   }

 // add the value 10, 20, 30 ... 80, 90
 for ( int i = 1 ; i < 10 ; i++ )
   {
    push ( s1, i * 10 );
   }

 // remove all of the values from the stack
 // note the values are removed in the reverse of 
 //   how they were pushed onto the stack
 while ( isEmpty ( s1 ) == false )
   {
     cout << top ( s1 ) << endl ;
     pop ( s1 );
   }

 // prompt the user to enter some values
 // quit when a negative value is entered
 // push all non-negative values onto the stack
 int val;

 do 
 {
   cout << "Enter a value to push onto the stack (negative to stop): " ;
   cin >> val;

   if (val >= 0)
     push (s1, val);
 } while ( val >= 0 );

 // remove all of the values from the stack
 // note the values are removed in the reverse of 
 //   how they were pushed onto the stack
 while ( isEmpty ( s1 ) == false )
   {
     cout << top ( s1 ) << endl ;
     pop ( s1 );
   }


 return 1;
}