the stack data abstraction

#define LIMIT 50

typedef binarytreepointer whatever;

typedef struct

{

whatever stackarray[LIMIT];

int top;

}stack;

#define TRUE 1

#define FALSE 0

setstack(ps)

/* Sets the stack s to empty. */

stack *ps;

{

(*ps).top = -1;

}

empty(ps)

/* Returns true only if stack s is empty.*/

stack *ps;

{

return((*ps).top == -1);

}

push(value,ps)

/* Inserts value at the top of stack s. */

whatever value;

stack *ps;

{

if ((*ps).top == (LIMIT - 1))

overflow(ps);

else

{

(*ps).top = (*ps).top + 1;

(*ps).stackarray[(*ps).top] = value;

}

}

pop(ps,pvalue)

/* Removes the top entry of stack s

and copies its contents into value.

*/

stack *ps;

whatever *pvalue;

{

if (empty(ps))

underflow(ps);

else

{

*pvalue = (*ps).stackarray[(*ps).top];

(*ps).top = (*ps).top - 1;

}

}

whatever item(ps)

/* Returns a copy of the top entry on stack s. */

stack *ps;

{

return((*ps).stackarray[(*ps).top]);

}

last(ps)

/* Returns true only if stack s

contains no non null pointers.

*/

stack *ps;

{

int i,temp;

binarytreepointer null,setnull();

null = setnull();

temp = TRUE;

for (i=0;i<=(*ps).top;i++)

if ((*ps).stackarray[i] != null)

temp = FALSE;

return(temp);

}

overflow(ps)

/* Prints a message if the stack overflows. */

stack *ps;

{

printf("\n stack overflow ");

}

underflow(ps)