CS 201 - 9/4/2014

/* actual C code */
#define TRUE 1
#define FALSE 0
#define EMPTYPOS 0

typedef struct StackStruct Stack;

struct StackStruct
{
   int arr[10];
   int max; 
   int top;
};

---------------
int main ()
{
   Stack st1;
   Stack st2;

   /* initialize the stack variable instance */
   /* inline init of st1 */
   int i;
   st1.max = 10;
   st1.top = 0;
   for (i = 0 ; i < st1.max ; i++)
      st1.arr[i] = -999;

  /* function initial call */
  stackInit (&st2);

  /* function call for isEmpty()  */
  if ( isEmpty(st1) == TRUE )
    .....

  while ( isEmpty(st2) == FALSE )
    ......

  push (&st1, 8);
  push (&st1, 15);
  push (&st1, 2);

  val = top (st1);

  pop (&st1);



----------------------------
/* code for stackInit() called from main */

void stackInit (Stack* pst)
{
  int i;

  (*pst).max = 10;
  (*pst).top = 0;
 
  for (i = 0 ; i < (*pst).max ; i++)
       (*pst).arr[i] = -999;
}

/* alternitive syntax for the dereference syntax */
void stackInit (Stack* pst)
{
  int i;

  pst->max = 10;
  pst->top = 0;
 
  for (i = 0 ; i < pst->max ; i++)
       pst->arr[i] = -999;
}


/* code for isEmpty()  */

int isEmpty (Stack pst)
{ 
   if ( pst.top == 0 )
      return TRUE;
   else
      return FALSE;
}

int isEmpty (Stack pst)
{ 
   return (pst.top == 0);
}

/* valid but less safe */
int isEmpty (Stack pst)
{ 
   return !pst.top;
}

----------------------------------
/* push - adds a value to the stack

void push (Stack* pst, int val)
{
   /* verify that room exists on the stack *
   if (pst->top == pst->max )
      {
       /* error */
       return ;
      }

   /* add the value to the top of the stack */
   pst->arr[ pst->top ] = val;

   pst->top++;
}

int top (Stack pst)
{
   return (pst.arr[pst.top-1]);
}

void pop (Stack* pst)
{
   /* verify the stack is NOT empty */
   if ( isEmpty(*pst) == TRUE)
     {
       /* error */
       return;
     }

   pst->top--;
   pst->arr[pst->top] = -999;
}